Vaxcyte (PCVX) 10-K 28 Feb 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 23, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	PCVX
Entity Registrant Name	VAXCYTE, INC.
Entity Central Index Key	0001649094
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity File Number	001-39323
Entity Tax Identification Number	46-4233385
Entity Address, Address Line One	825 Industrial Road
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	San Carlos
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94070
City Area Code	650
Local Phone Number	837-0111
Entity Common Stock, Shares Outstanding		56,310,751
Entity Public Float			$ 788.6
Document Annual Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Common Stock, $0.001 par value per share
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	Part III incorporates information by reference from the Registrant’s definitive proxy statement to be filed with the U.S. Securities and Exchange Commission pursuant to Regulation 14A, not later than 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K, in connection with the Registrant’s 2022 annual meeting of stockholders.
Auditor Name	Deloitte & Touche LLP
Auditor Location	San Francisco, California
Auditor Firm ID	34

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 68,985	$ 386,200
Short-term investments	176,985
Prepaid expenses and other current assets	10,378	2,804
Total current assets	256,348	389,004
Property and equipment, net	7,954	3,272
Operating lease right-of-use assets	27,958
Long-term investments	27,117
Restricted cash	871
Other assets	4,089	550
Total noncurrent assets	67,989	3,822
Total assets	324,337	392,826
Current liabilities:
Accounts payable	6,758	29,785
Accrued compensation	3,455	284
Accrued manufacturing expenses	4,440	13,012
Accrued expenses (including related party accrual of $0 and $677 as of December 31, 2021 and December 31, 2020, respectively)	8,787	3,766
Deferred rent - current		14
Operating lease liabilities — current	5,276
Total current liabilities	28,716	46,861
Deferred rent - long-term		10
Operating lease liabilities — long-term	11,507
Other liabilities	96	112
Total liabilities	40,319	46,983
Commitments and contingencies (Note 6)
Stockholders' Equity
Preferred stock, $0.001 par value — 10,000,000 authorized at December 31, 2021 and December 31, 2020; no shares issued and outstanding at December 31, 2021 and December 31, 2020
Common stock, $0.001 par value - 500,000,000 shares authorized at December 31, 2021 and December 31, 2020;53,031,978 and 51,071,593 shares issued and outstanding at December 31, 2021 and December 31, 2020, respectively	56	54
Additional paid-in capital	582,844	544,353
Accumulated other comprehensive loss	(241)
Accumulated deficit	(298,641)	(198,564)
Total stockholders' equity	284,018	345,843
Total liabilities, redeemable convertible preferred stock and stockholders' equity	$ 324,337	$ 392,826

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Related party accrual	$ 0	$ 677
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	53,031,978	51,071,593
Common stock, shares outstanding	53,031,978	51,071,593

Statements of Operations

Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating expenses:
Research and development (including related party expenses of $2359, $1,331 and $1,137 in 2021, 2020 and 2019, respectively)	$ 78,411	$ 73,564	$ 45,607
General and administrative	25,259	16,017	8,546
Total operating expenses	103,670	89,581	54,153
Loss from operations	(103,670)	(89,581)	(54,153)
Other income (expense), net:
Interest expense	(7)	(7)	(40)
Interest income	344	244	632
Grant income	1,585	2,478	237
Realized gains on marketable securities	2
Foreign currency transaction gains (losses)	1,669	(2,351)	(135)
Change in fair value of the redeemable convertible preferred stock tranche liability			3,185
Total other income (expense), net	3,593	364	3,879
Net loss	$ (100,077)	$ (89,217)	$ (50,274)
Net loss per share, basic and diluted	$ (1.93)	$ (3.02)	$ (13.25)
Weighted-average shares outstanding, basic and diluted	51,922,108	29,545,810	3,795,090

Statements of Operations (Paren

Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Research and development expense to related party	$ 2,359	$ 1,331	$ 1,137

Statements of Comprehensive Los

Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net Loss	$ (100,077)	$ (89,217)	$ (50,274)
Other comprehensive loss:
Unrealized losses on investments	(241)
Comprehensive Loss	$ (100,318)	$ (89,217)	$ (50,274)

Statements of Redeemable Conver

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Common StockIPO	Common StockMarket offering	Additional Paid-in Capital	Additional Paid-in CapitalIPO	Additional Paid-in CapitalMarket offering	Accumulated Deficit	Accumulated Other Comprehensive Loss	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Series C Redeemable Convertible Preferred Stock	Series D Redeemable Convertible Preferred Stock
Beginning balance at Dec. 31, 2018	$ (57,728)	$ 6			$ 1,339			$ (59,073)
Beginning balance, shares at Dec. 31, 2018										6,225,719	6,786,896	3,688,740
Beginning balance at Dec. 31, 2018										$ 24,967	$ 55,151	$ 37,692
Beginning balance, shares at Dec. 31, 2018		3,757,403
Issuance of preferred stock												$ 42,500
Issuance of preferred stock, net of issuance cost (in shares)												3,688,740
Exercise of stock options	322	$ 1			321
Exercise of stock options (in shares)		243,230
Issuance of common stock related to early exercised stock options		59,276
Vesting of early exercised stock options	122				122
Stock-based compensation expense	1,185				1,185
Net Loss	(50,274)							(50,274)
Ending balance at Dec. 31, 2019	(106,373)	$ 7			2,967			(109,347)
Ending balance, shares at Dec. 31, 2019										6,225,719	6,786,896	7,377,480
Ending balance at Dec. 31, 2019										$ 24,967	$ 55,151	$ 80,192
Ending balance, shares at Dec. 31, 2019		4,059,909
Conversion of preferred stock	270,190	$ 29			270,161					$ (24,967)	$ (55,151)	$ (80,192)	$ (109,879)
Conversion of preferred stock (in shares)										(6,225,719)	(6,786,896)	(7,377,480)	(8,220,242)
Conversion of preferred stock (in shares)		28,610,337
Conversion of common stock warrant		30,278
Conversion of preferred stock warrant		16,591
Warrant liability write-off	629				629
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs	264,007		$ 18			$ 263,989
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs (in shares)			17,968,750
Issuance of common stock under Employee Stock Purchase Plan	374				374
Issuance of common stock under Employee Stock Purchase Plan (in shares)		27,465
Issuance of preferred stock													$ 109,879
Issuance of preferred stock, net of issuance cost (in shares)													8,220,242
Exercise of stock options	635				635
Exercise of stock options (in shares)		343,444
Issuance of common stock related to early exercised stock options		14,819
Vesting of early exercised stock options	164				164
Stock-based compensation expense	5,434				5,434
Net Loss	(89,217)							(89,217)
Ending balance at Dec. 31, 2020	345,843	$ 54			544,353			(198,564)
Ending balance, shares at Dec. 31, 2020		51,071,593
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs	13,847			$ 1			$ 13,846
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs (in shares)				567,045
Issuance of common stock under Employee Stock Purchase Plan	888				888
Issuance of common stock under Employee Stock Purchase Plan (in shares)		62,546
Exercise of stock options	3,012				3,012
Exercise of stock options (in shares)		931,114
Issuance of common stock to LonzaLtd.	10,001	$ 1			10,000
Issuance of common stock to Lonza Ltd. (in shares)		399,680
Unrealized losses on investment	(241)								$ (241)
Vesting of early exercised stock options	16				16
Stock-based compensation expense	10,729				10,729
Net Loss	(100,077)							(100,077)
Ending balance at Dec. 31, 2021	$ 284,018	$ 56			$ 582,844			$ (298,641)	$ (241)
Ending balance, shares at Dec. 31, 2021		53,031,978

Statements of Redeemable Conv_2

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Market offering
Issuance costs	$ 479
Common Stock | IPO
Issuance costs		$ 3,368
Series C Redeemable Convertible Preferred Stock
Issuance costs			$ 0
Series D Redeemable Convertible Preferred Stock
Issuance costs		$ 121

Statements of Cash Flows (Unaud

Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (100,077)	$ (89,217)	$ (50,274)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,800	1,405	1,232
Stock-based compensation expense	10,729	5,434	1,185
Change in fair value of redeemable convertible preferred stock warrant		179	(12)
Change in fair value of redeemable convertible preferred stock tranche liabilities			(3,185)
Loss on disposal of assets	97	34	1
Asset impairment charges	0	267	0
Amortization of operating right-of-use assets	1,657
Net amortization of premiums on investments	1,406
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(7,369)	(58)	(1,070)
Other assets	(3,539)	(75)	120
Operating lease liabilities	(12,856)
Accounts payable	(12,470)	26,102	868
Accrued compensation	3,170	(130)	(775)
Accrued manufacturing expenses	(8,572)	7,235	3,970
Accrued expenses	4,631	2,207	718
Deferred rent and other long-term liabilities		(11)	77
Net cash used in operating activities	(121,393)	(46,628)	(47,145)
Cash flows from investing activities:
Purchases of property and equipment	(6,555)	(1,155)	(1,195)
Purchases of investments	(336,341)
Maturities of investments	100,500
Sales of investments	30,062
Proceeds from sales of property and equipment	26	50
Net cash used in investing activities	(212,308)	(1,105)	(1,195)
Cash flows from financing activities:
Payments of capital lease obligations		(61)	(278)
Proceeds from initial public offering, net of underwriters' commissions and discounts		267,375
Payment of issuance costs for initial public offering		(3,368)
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs		109,879	42,500
Proceeds from exercise of common stock options	3,012	635	322
Proceeds from issuance of common stock under ATM Sales Program, net of issuance costs	13,896
Proceeds from issuance of common stock related to early exercised stock options		36	120
Proceeds from issuance of common stock under the Employee Stock Purchase Plan	888	374
Payments of deferred offering costs			(1,097)
Net cash provided by financing activities	17,796	374,870	41,567
Effect of exchange rate changes on cash and cash equivalents	(439)	87	(341)
Net (decrease) increase in cash, cash equivalents and restricted cash	(316,344)	327,224	(7,114)
Cash, cash equivalents and restricted cash, beginning of period	386,200	58,976	66,090
Cash, cash equivalents and restricted cash, end of period	69,856	386,200	58,976
Supplemental disclosure of cash flow information:
Cash paid for interest	7	7	40
Supplemental disclosures of non-cash investing and financing activities:
Purchases of property and equipment recorded in accounts payable and accrued expenses	766	494	21
Conversion of convertible preferred stock into common stock		270,190
Stock issued for payment of accounts payable	$ 10,001
Deferred offering costs included in accounts payable and accrued expenses		$ 134	$ 33

Company Organization and Nature

Company Organization and Nature of Business	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company Organization and Nature of Business	1. Company Organization and Nature of Business Vaxcyte, Inc. (“we,” “us,” “the Company,” or “Vaxcyte”), headquartered in San Carlos, California, was incorporated in the state of Delaware on November 27, 2013 as SutroVax, Inc. and we changed our name to Vaxcyte, Inc. on May 15, 2020. We are a clinical-stage vaccine innovation company engineering high-fidelity vaccines to protect humankind from the consequences of bacterial diseases. We are developing broad-spectrum conjugate and novel protein vaccines to prevent or treat bacterial infectious diseases. We are re-engineering the way highly complex vaccines are made through modern synthetic techniques, including advanced chemistry and the XpressCF cell-free protein synthesis platform, exclusively licensed from Sutro Biopharma, Inc. Unlike conventional cell-based approaches, our system for producing difficult-to-make proteins and antigens is intended to accelerate our ability to efficiently create and deliver high-fidelity vaccines with enhanced immunological benefits . Our pipeline includes pneumococcal conjugate vaccine (“PCV”) candidates that we believe are among the most broad-spectrum PCV candidates currently in development, targeting the approximately $ 7 billion global pneumococcal vaccine market. Our lead vaccine candidate, VAX-24, is a 24-valent broad-spectrum investigational PCV being developed for the prevention of invasive pneumococcal disease, or IPD , and pneumonia. On January 6, 2022, we announced that the U.S. Food and Drug Administration, or FDA, cleared our investigational new drug, or IND, application for VAX-24 in adults. On February 23, 2022, we announced the initiation of our Phase 1/2 clinical proof-of-concept study in adults 18 to 64 years of age. We expect to announce topline safety, tolerability and immunogenicity results from this study by the end of 2022. Pending the successful completion of the Phase 1 portion of this study, we expect to begin enrollment in a separate Phase 2 study in healthy adults aged 65 and older and to announce topline safety, tolerability and immunogenicity results from this study in the first half of 2023. Subject to a pre-IND meeting with the FDA and the successful topline results of the Phase 1/2 proof-of-concept study in adults 18-64 years of age, we anticipate submitting a pediatric IND application to the FDA for VAX-24 in the first half of 2023. Our second PCV candidate, VAX-XP, leverages our scalable and modular platform and builds on the technical proof of concept established by VAX-24 and is designed to expand the breadth of coverage to greater than 30 strains without compromising immunogenicity due to carrier suppression. In addition to our PCV franchise, our pipeline includes VAX-A1, a novel conjugate vaccine candidate designed to prevent Group A Strep; VAX-PG, a novel protein vaccine candidate targeting the keystone pathogen responsible for periodontitis; and other discovery-stage programs. Our primary activities since incorporation have been to perform research and development, undertake preclinical studies and conduct manufacturing activities in support of our product development efforts; organize and staff the Company; establish our intellectual property portfolio; and raise capital to support and expand such activities. Reverse Stock Split On June 5, 2020, we filed a certificate of amendment to our amended and restated certificate of incorporation to effect a one-for-1.6870 reverse stock split of our issued and outstanding common stock, preferred stock, stock options and warrants effective on June 5, 2020. Accordingly, all share and per share amounts for all periods presented in the financial statements and notes thereto have been retroactively adjusted. Initial Public Offering In June 2020, we completed an initial public offering (“IPO”) in which we issued and sold 17,968,750 shares of common stock, including shares issued upon the exercise in full of the underwriters’ option to purchase 2,343,750 additional shares of common stock, at a public offering price of $ 16.00 per share. We received $ 264.0 million in net proceeds, after deducting underwriting discounts and commissions of $ 20.1 million and offering expenses of $ 3.4 million. Immediately prior to the completion of our IPO, all outstanding shares of redeemable convertible preferred stock were converted into 28,610,337 shares of common stock. Subsequent to the completion of the IPO, there were no shares of redeemable convertible preferred stock outstanding.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	2. Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation These financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding annual reporting. Certain changes in presentation were made in these financial statements as of and for the year ended December 31, 2019 to conform to the presentation as of and for the years ended December 31, 2021 and 2020. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities at the date of the financial statements. On an ongoing basis, we evaluate our estimates and assumptions, including those related to stock-based compensation expense, accruals for certain research and development costs, the incremental borrowing rate, the valuation of deferred tax assets and income taxes. Management bases our estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject us to a concentration of credit risk consist primarily of cash and cash equivalents and investments. We invest in money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt, commercial paper and asset-backed securities. We maintain bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. We are exposed to credit risk in the event of a default by the financial institutions holding our cash and issuers of investments to the extent recorded on the balance sheets. Our investment policy limits investments to money market funds, certain types of debt securities issued by the U.S. Government and its agencies, corporate debt, commercial paper and asset-backed securities, and places restrictions on the credit ratings, maturities and concentration by type and issuer. We have not experienced any significant losses on our deposits of cash, cash equivalents or investments. We are subject to supplier concentration risk from our suppliers. We source our critical raw materials from a sole source supplier, Sutro Biopharma, Inc. (“Sutro Biopharma”). We also use one contract manufacturing organization (“CMO”), Lonza Ltd. (“Lonza”), to handle most of our manufacturing activities. If we were to experience disruptions in raw materials supplied by Sutro Biopharma, or in manufacturing activities at Lonza, we may experience significant delays in our product development timelines and may incur substantial costs to secure alternative sources of raw materials or manufacturing. Our future results of operations involve a number of other risks and uncertainties. Factors that could affect our future operating results and cause actual results to vary materially from expectations include, but are not limited to: our early stages of clinical vaccine development; our ability to advance vaccine candidates into, and successfully complete, clinical trials on the timelines we project; our ability to adequately demonstrate sufficient safety and efficacy of our vaccine candidates; our ability to enroll subjects in our ongoing and future clinical trials; our ability to successfully manufacture and supply our vaccine candidates for clinical trials; our ability to obtain additional capital to finance our operations; our ability to obtain, maintain and protect our intellectual property rights; developments relating to our competitors and our industry, including competing vaccine candidates; general and market conditions; and other risks and uncertainties, including those more fully described in the “Risk Factors” section of this Annual Report on Form 10-K. Segment and Geographical Information We operate and manage our business as one reportable and operating segment. Our chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. All of our long-lived assets are based in the United States. Long-lived assets are comprised of property and equipment. Cash, Cash Equivalents and Restricted Cash We consider all highly liquid investments purchased with original maturities of three months or less from the date of purchase to be cash and cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and commercial paper and are stated at their fair values. Restricted cash consists of a standby letter of credit, which was issued in the first quarter of 2021, that serves as collateral for the lease agreement for our new corporate headquarters. Cash, cash equivalents and restricted cash as reported within the statement of cash flows consisted of the following: Years Ended December 31, 2021 2020 2019 (in thousands) Cash and cash equivalents $ 68,985 $ 386,200 $ 58,976 Restricted cash 871 — — Cash, cash equivalents and restricted cash $ 69,856 $ 386,200 $ 58,976 Investments Our investments have been classified and accounted for as available-for-sale securities. Our investments consist of U.S. Treasury securities, U.S. government agency securities, corporate debt, commercial paper and asset-backed securities. These securities are recorded on the balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive loss. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income (expense), net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income (expense), net. We evaluate securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are included in other income (expense), net. We classify our investments as short or long term primarily based on the remaining contractual maturity of the securities. Deferred Offering Costs Deferred offering costs consist of fees and expenses incurred in connection with the sale of our common stock in equity transactions, including legal, accounting, printing and other issuance-related costs. Prior to the completion of equity transactions, deferred offering costs are included in Other assets on the balance sheet. In connection with and as of the closing of equity transactions, these costs are reclassified to Additional paid-in capital, representing a reduction to the gross proceeds. As of December 31, 2020, $ 3.4 million of IPO-related costs were included in the Additional paid-in capital line item on the balance sheet. As of December 31, 2021 and 2020, $ 0.5 million and $ 0.1 million of deferred offering costs, respectively, were included in Other assets on the balance sheet. Property and Equipment, Net Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally three to five years . Leasehold improvements are amortized over the shorter of the expected life or lease term. Repairs and maintenance expenditures, which are not considered improvements and do not extend the useful life of property and equipment, are expensed as incurred. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in the statements of operations in the period realized. Leases Under Financial Accounting Standards Board (FASB) Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) and its associated amendments (“ASC 842”), we determine if an arrangement is a lease at inception. In addition, we determine whether a lease meets the classification criteria of a finance or operating lease at the lease commencement date considering whether: (i) the lease transfers ownership of the underlying asset to the lessee at the end of the lease term; (ii) the lease grants the lessee an option to purchase the underlying asset that the lessee is reasonably certain to exercise; (iii) the lease term is for a major part of the remaining economic life of the underlying asset; (iv) the present value of the sum of the lease payments and residual value guaranteed by the lessee equals or exceeds substantially all of the fair value of the underlying asset; and (v) the underlying asset is such a specialized nature that it is expected to have no alternative use to the lessor at the end of the lease term. As of December 31, 2021, our lease population consisted of real estate operating leases. As of December 31, 2021 , we did no t have any finance leases. Operating leases are included in Operating lease right-of-use (ROU) assets, Operating lease liabilities — current and Operating lease liabilities — long term in our balance sheet. ROU assets represent our right to use the underlying assets for the lease term and lease liabilities represent our obligation to make lease payments arising from the leases. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, if the rate implicit in the lease is not readily determinable, we use our incremental borrowing rate based on the information available at the lease commencement date. We determine the incremental borrowing rate based on an analysis of corporate bond yields with a credit rating similar to us. The determination of our incremental borrowing rate requires management judgment, including development of a synthetic credit rating and cost of debt, as we currently do not carry any debt. We believe that the estimates used in determining the incremental borrowing rate are reasonable based upon current facts and circumstances. Applying different judgment to the same facts and circumstances could yield a different incremental borrowing rate. The operating lease ROU assets also include adjustments for prepayments and accrued lease payments and exclude lease incentives. ROU assets and lease liabilities may include options to extend or terminate leases if it is reasonably certain that we will exercise such options. Lease payments which are fixed and determinable are amortized as rent and lease expense on a straight-line basis over the expected lease term. Variable lease costs, which are dependent on usage, a rate or index, including common area maintenance charges, are expensed as incurred. Lease agreements that include lease and non-lease components are accounted for as a single lease component. Lease agreements with non-cancelable terms of less than 12 months are not recorded on our balance sheets. Impairment of Long-Lived Assets We review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparing the carrying amount to the future undiscounted net cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows generated by the assets. There were $ 0 , $ 0.3 million, and $ 0 of impairments of long-lived assets during the years ended December 31, 2021, 2020 and 2019, respectively. Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of our financial instruments, including cash and cash equivalents, prepaid and other current assets, accounts payable, accrued expenses, and other liabilities, approximate fair value due to their short-term maturities. Prior to their automatic conversion upon our IPO in June 2020, the redeemable convertible preferred stock tranche liability and redeemable convertible preferred stock warrant were carried at fair value (see Note 3). Research and Development Research and development costs are expensed as incurred. Research and development costs include salaries, stock-based compensation and benefits for employees performing research and development activities, an allocation of facility and overhead expenses, expenses incurred under agreements with consultants, CMOs, contract research organizations (“CROs”) and investigative sites that conduct preclinical studies, other supplies and costs associated with product development efforts, preclinical activities and regulatory operations. Accrued Research and Development We have entered into various agreements with CROs and CMOs. Our research and development accruals, which include accrued manufacturing expenses, are estimated based on the level of services performed, progress of the studies, including the phase or completion of events, and contracted costs. The estimated costs of research and development services provided, but not yet invoiced, are included in accrued expenses on the balance sheet. If the actual timing of the performance of services or the level of effort varies from the original estimates, we will adjust the accrual accordingly. Payments made to CROs or CMOs under these arrangements in advance of the performance of the related services are recorded as prepaid expenses and other current assets until the services are rendered. To date, there have been no material differences between our estimates of such expenses and the amounts actually incurred. Income Taxes We account for income taxes using the asset and liability method. We recognize deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover our deferred income tax assets, we consider all available positive and negative evidence, including our operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event we determine that we would be able to realize our deferred income tax assets in the future in excess of their net recorded amount, we would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2021 and 2020, we have recorded a full valuation allowance on our deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained during an audit. Interest and penalties related to unrecognized tax benefits are included within the provision for income tax. Stock-Based Compensation Expense For options granted to employees, non-employees, and directors, stock-based compensation is measured at grant date based on the fair value of the award. We determine the grant-date fair value of the options using the Black-Scholes option-pricing model. The grant-date fair value of awards is amortized over the employees’ requisite service period or the non-employees’ vesting period as the services are rendered. Forfeitures are accounted for as they occur. Additionally, our 2020 Employee Stock Purchase Plan is deemed to be a compensatory plan and is therefore included in stock-based compensation expense. Comprehensive Loss Comprehensive loss includes net loss and other comprehensive loss for the period. Other comprehensive loss consists of unrealized loss on investments. Foreign Currency Transactions Transactions denominated in foreign currencies are initially measured in U.S. dollars using the exchange rate on the date of the transaction. Foreign currency denominated monetary assets and liabilities are subsequently re-measured at the end of each reporting period using the exchange rate at that date, with the corresponding foreign currency transaction gain or loss recorded in the statements of operations and statements of cash flows. Nonmonetary assets and liabilities are not subsequently re-measured. Net Loss Per Share Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common stock outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, redeemable convertible preferred stock, redeemable convertible preferred stock warrant, common stock subject to repurchase, and stock options are considered to be potentially dilutive securities. Basic and diluted net loss attributable to common stockholders per share is presented in conformity with the two-class method required for participating securities as the redeemable convertible preferred stock is considered a participating security. Our participating securities do not have a contractual obligation to share in our losses. As such, the net loss was attributed entirely to common stockholders. Because we have reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . ASU 2016-02 was subsequently amended by ASU 2018-01, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2019-10 and ASU 2020-05, which the FASB issued in January 2018, July 2018, July 2018, December 2018, March 2019, November 2019 and June 2020, respectively (collectively, “ASC 842”). ASC 842 requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new standard establishes a ROU model that requires a lessee to recognize a ROU asset and a lease liability on the balance sheet for all leases with a term longer than 12 months. Under ASC 842, leases are classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement. We early adopted the new standard effective January 1, 2021 using the modified retrospective transition approach. Upon adoption on January 1, 2021, we recognized ROU assets and lease liabilities totaling $ 0.9 million and $ 0.9 million, respectively, to reflect the present value of remaining lease payments under existing lease arrangements. The difference between the leased assets and lease liabilities represents the existing deferred rent liabilities balance resulting from historical straight-lining of operating leases for our facilities, which was reclassified upon adoption to reduce the measurement of the leased assets. The balance of our deferred rent liabilities, which was reclassified to reduce the ROU assets upon adoption, was immaterial . We applied the modified retrospective transition approach and did not recast prior periods. Although we applied this approach, we did not have a cumulative effect adjustment to the opening balance of our retained deficit upon adoption. As permitted by the standard, we elected the transition practical expedient package, which among other things, allowed the carryforward of historical lease classifications. For additional details regarding the impact of adoption and disclosure, see Note 5, “Leases, " to our financial statements included in Part II, Item 8 of this Annual Report on Form 10-K. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740) . The amendments in ASU 2019-12 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify U.S. GAAP or other areas of Topic 740 by clarifying and amending existing guidance. The new standard was effective for us on January 1, 2021 and for interim periods within 2021. The adoption of ASU 2019-12 did not have a material impact on our financial statements. Recently Issued Accounting Pronouncements—Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments and has subsequently issued related amendments, collectively referred to as “Topic 326.” Topic 326 requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. We are currently assessing the impact of this standard to our financial statements and related disclosures. In November 2021, the FASB issued ASU 2021-10, Government Assistance (Topic 832): Disclosure by Business Entities about Government Assistance, which requires disclosures about transactions with a government entity that are accounted for by applying a grant or contribution accounting model by analogy to other accounting guidance, such as a grant model within International Accounting Standard 20, Accounting for Government Grants and Disclosure of Government Assistance , or Subtopic 958-605, Not-For-Profit Entities - Revenue Recognition . The required disclosures include (i) the nature of the transactions and the related accounting policy used to account for the transactions, (ii) the financial statement line items that are affected by the transactions and (iii) the significant terms and conditions of the transactions, including commitments and contingencies. This standard is effective for annual periods beginning after December 15, 2021, with early adoption and retrospective or prospective application permitted. This standard is effective for us on January 1, 2022 and only impacts annual financial statement footnote disclosures . In Note 11, "Funding Arrangement," to our financial statements included in Part II, Item 8 of this Annual Report on Form 10-K, we included disclosures on our cost-reimbursement research award from CARB-X. Therefore, we do not believe the adoption of this standard will have a material impact on our financial statements.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	3. Fair Value Measurements and Fair Value of Financial Instruments Assets and liabilities recorded at fair value on a recurring basis in the balance sheets, as well as assets and liabilities measured at fair value on a non-recurring basis or disclosed at fair value, are categorized based upon the level of judgment associated with inputs used to measure their fair values. The accounting guidance for fair value provides a framework for measuring fair value and requires certain disclosures about how fair value is determined. Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance also establishes a three-level valuation hierarchy that prioritizes the inputs to valuation techniques used to measure fair value based upon whether such inputs are observable or unobservable. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect market assumptions made by the reporting entity. The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows: Level 1— Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2— Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 — Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. Level 1 securities consist of highly liquid money market funds for which the carrying amounts approximate their fair values due to their short maturities. U.S. Treasury securities are valued using Level 1 inputs based on unadjusted, quoted prices in active markets that are observable at the measurement date for identical assets or liabilities. Level 2 securities, consisting of corporate debt, commercial paper, U.S. government agency securities and asset-backed securities, are measured based on other observable inputs, including broker or dealer quotations or alternative pricing sources. When quoted prices in active markets for identical assets or liabilities are not available, we rely on non-binding quotes from our investment managers, which are based on proprietary valuation models of independent pricing services. These models generally use inputs such as observable market data, quoted market prices for similar instruments or historical pricing trends of securities relative to our peers. To validate the fair value determinations provided by our investment managers, we review the pricing movement in the context of overall market trends and trading information from our investment managers. In addition, we assess the inputs and methods used in determining the fair value in order to determine the classification of securities in the fair value hierarchy. We had no Level 3 securities either as of December 31, 2021 or 2020. There were no transfers within the hierarchies during the years ended December 31, 2 0 21 or 2020. We invested in money market funds as of December 31, 2020. In January 2021, we started to invest some of our funds in corporate debt, commercial paper, U.S. Treasury securities, U.S. government agency securities and asset-backed securities in addition to money market funds. The following tables set forth our financial instruments measured at fair value on a recurring basis by level within the fair value hierarchy at December 31, 2021 and 2020: December 31, 2021 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 27,834 $ — $ — $ 27,834 Money market funds Level 1 17,555 — — 17,555 Commercial paper Level 2 23,597 — ( 1 ) 23,596 Total cash and cash equivalents $ 68,986 $ — $ ( 1 ) $ 68,985 Investments: U.S. Treasury securities Level 1 45,290 — ( 73 ) 45,217 Commercial paper Level 2 61,941 — ( 22 ) 61,919 Corporate debt Level 2 58,498 — ( 74 ) 58,424 Asset backed securities Level 2 13,899 ( 25 ) 13,874 U.S. government agency securities Level 2 24,714 — ( 46 ) 24,668 Total investments 204,342 — ( 240 ) 204,102 Total assets measured at fair value $ 273,328 $ — $ ( 241 ) $ 273,087 December 31, 2020 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 4,788 $ — $ — $ 4,788 Money market funds Level 1 381,412 — — 381,412 Total assets measured at fair value $ 386,200 $ — $ — $ 386,200 The following table presents the contractual maturities of our investments as of December 31, 2021 (in thousands): December 31, 2021 Fair Value Due in less than one year $ 176,985 Due in one to five years 27,117 Total $ 204,102

Balance Sheet Details

Balance Sheet Details	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Details	4. Balance Sheet Details Property and Equipment, Net Property and equipment, net as of December 31, 2021 and 2020 consisted of the following: December 31, 2021 2020 (in thousands) Furniture and equipment $ 1,619 $ 397 Computers and computer software 430 111 Lab equipment 9,453 4,739 Leasehold improvements — 1,903 Construction in progress — 219 Total property and equipment 11,502 7,369 Less: accumulated depreciation and amortization ( 3,548 ) ( 4,097 ) Property and equipment, net $ 7,954 $ 3,272 Depreciation and amortization expense for years ended December 31, 2021, 2020 and 2019 was $ 1.8 million, $ 1.4 million and $ 1.2 million respectively, of which $ 0 , $ 0 and $ 0.2 million related to capital lease amortization expense for the years ended December 31, 2021, 2020 and 2019, respectively. Accrued Expenses Accrued expenses as of December 31, 2021 and 2020 consisted of the following: December 31, 2021 2020 (in thousands) Preclinical studies $ 5,039 $ 2,844 Professional fees 400 490 Other accrued expenses 3,348 432 Total $ 8,787 $ 3,766

Leases

Leases	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leases	5. Leases Operating Lease Obligations In July 2016, we entered into a five-year lease agreement for our previous headquarters facility located in Foster City, California. The original term of the lease was from September 1, 2016 to August 31, 2021 , with two 30 -month renewal options . In July 2019, we leased another facility in Foster City, California as a result of growth in personnel and lab space requirements. The original term of this lease was from July 1, 2019 to October 31, 2021 , with no renewal options . In November 2020, we extended the terms of both of these leases for six months to March 1, 2022 and April 30, 2022 , respectively. In February 2022, we entered into an early termination agreement for one of the facilities in Foster City and terminated our lease on February 12, 2022 instead of April 30, 2022. We also leased an office in San Diego, California with a lease term that ended on April 30, 2021 . In January 2021, we entered into a lease agreement for our new corporate headquarters facility located in San Carlos, California and a license agreement for temporary lab and office space in Palo Alto, California. The lease term for our new corporate headquarters facility began on January 22, 2021 and expires on December 31, 2025 . We have two 60 -month renewal options. The original term of the license agreement for temporary space in Palo Alto terminated when the San Carlos office leasehold improvements were completed and we moved into our new corporate headquarters. We extended the license agreement for the Palo Alto office by 60 days to March 3, 2022 to accommodate our relocation plan. These two agreements are accounted for as a combined lease because the contracts were negotiated as a package with the same commercial objective. We early adopted ASC 842 and its associated amendments as of January 1, 2021 using the modified retrospective transition approach by applying the new standard to all leases existing at the date of the initial adoption and not restating comparative periods. We elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed us to carryforward the historical lease classification of those leases in place as of January 1, 2021. The adoption of ASC 842 resulted in an increase to total assets and liabilities due to the recording of operating lease ROU assets and operating lease liabilities of $ 0.9 million and $ 0.9 million, respectively, as of January 1, 2021. ROU assets and lease liabilities are recognized based on the present value of the fixed and in-substance fixed lease payments over the lease terms at their respective commencement dates. The ROU assets also include any initial direct costs incurred and lease payments made at or before the commencement date and are reduced by lease incentives. In determining the present value of lease payments, since the rate implicit in the lease is generally not readily determinable, we use our incremental borrowing rate, which requires management’s judgment, including for the development of a synthetic credit rating and the cost of debt as we currently do not carry any debt. Variable lease costs, which are dependent on usage, a rate or index, including common area maintenance charges for our real estate leases, are expensed as incurred. Upon commencement of the Palo Alto lease in March 2021, we recorded a ROU asset and lease liability of $ 0.3 million and $ 0.3 million, respectively. Upon commencement of the San Carlos lease in December 2021, we recorded a ROU asset and lease liability of $ 28.4 million and $ 12.9 million, respectively. Because the Palo Alto and the San Carlos agreements are accounted for as a combined lease, lease payments and lease incentives are allocated between the two leases. Information related to our ROU assets and related lease liabilities was as follows (dollar amounts in thousands): December 31, 2021 Cash paid for operating lease liabilities $ 924 Right-of-use assets recognized in exchange for new lease obligations $ 27,958 Current operating lease liabilities $ 5,276 Non-current operating lease liabilities 11,507 Total lease liabilities $ 16,783 Weighted-average remaining lease term (in years) 3.75 Weighted-average discount rate 7.5 % Maturities of lease liabilities as of December 31, 2021 were as follows: Years ending December 31, (in thousands) 2022 (1) $ ( 105 ) 2023 6,639 2024 6,805 2025 6,976 Thereafter — Total future undiscounted lease payments 20,315 Less: Imputed interest ( 3,532 ) Total lease liabilities $ 16,783 _____________________________________________ (1) Maturities for 2022 are net of lease incentives of $ 0.9 million allocated to the Palo Alto office. Future minimum payments required under operating leases as of December 31, 2020 were as follows: Years ending December 31, (in thousands) 2021 $ 742 2022 190 Total future minimum payments $ 932 Rent expense recognized under the leases was $ 3.2 million, $ 0.7 million and $ 0.6 million for the years ended December 31, 2021, 2020 and 2019, respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Legal Contingencies From time to time, we may become involved in legal proceedings arising from the ordinary course of business. We record a liability for such matters when it is probable that future losses will be incurred and that such losses can be reasonably estimated. Significant judgment by us is required to determine both probability and the estimated amount. We do not believe that there is any litigation or asserted or unasserted claim pending that could, individually or in the aggregate, have a material adverse effect on our results of operations or financial condition. Guarantees and Indemnifications In the normal course of business, we enter into agreements that contain a variety of representations and provide for general indemnification. Our exposure under these agreements is unknown because it involves claims that may be made against us in the future. To date, we have not paid any claims or been required to defend any action related to our indemnification obligations. As of December 31, 2021, we did not have any material indemnification claims that were probable or reasonably possible and consequently have not recorded related liabilities. Indemnification To the extent permitted under Delaware law, we have agreed to indemnify our directors and officers for certain events or occurrences while the director or officer is, or was, serving at our request in such capacity. The indemnification period covers all pertinent events and occurrences during the director’s or officer’s service. The maximum potential amount of future payments we could be required to make under these indemnification agreements is not specified in the agreements; however, we have director and officer insurance coverage that reduces our exposure and enables us to recover a portion of any future amounts paid. We have not incurred any material costs as a result of such indemnification and are not currently aware of any indemnification claims. Development and Manufacturing Services Agreement On October 21, 2016, we entered into a development and manufacturing services agreement, as amended, with Lonza (the “Lonza DMSA”), pursuant to which Lonza is obligated to perform services including manufacturing process development and the manufacture of components for VAX-24, including the polysaccharide antigens, our proprietary eCRM protein carrier and conjugated drug substances. In the September 2017, we and Lonza agreed to defer the completion payments for any stage that commenced after December 31, 2019 or had not been completed by December 31, 2019 until the earlier of the completion of all Investigational New Drug (“IND”)-enabling activities or December 31, 2020. In March 2020, Lonza agreed to defer the completion payments until the earlier of the completion of all IND-enabling activities or April 30, 2021. In April 2021, Lonza further agreed to defer 50 % of the completion payments until the earlier of the completion of all IND-enabling activities or December 31, 2021. Pursuant to this agreement, all deferred completion payments were paid in December 2021. In June 2018, we and Lonza entered into a letter agreement pursuant to which we agreed to certain terms for potential future equity payments in shares of our common stock as partial satisfaction of future obligations to Lonza. This agreement states that the initial pre-IND cash payments would be subject to a specified dollar cap (the “Initial Cash Cap”). After the Initial Cash Cap has been reached, we have the option to make any further pre-IND payments owed to Lonza in cash, in shares of our common stock at then market prevailing prices, or a combination of both, at our election. The Initial Cash Cap had not been reached as of December 31, 2020. As such, no amount was recorded with respect to the potential future payments above the Initial Cash Cap at December 31, 2020. In April 2021, we reached the Initial Cash Cap and notified Lonza that we would be exercising our option to issue approximately $ 10.0 million in shares of our common stock as payment for a portion of pre-IND payments due April 30, 2021. In June 2021, we issued 399,680 shares of our common stock to Lonza at a price of $ 25.02 per share to pay for $ 10.0 million of the pre-IND payments due April 30, 2021. In October 2018, we entered into a second development and manufacturing services agreement with Lonza (the “Lonza 2018 DMSA,” and together with the Lonza DMSA, the “Lonza Agreements”), pursuant to which Lonza is obligated to perform services including manufacturing process development and the manufacture and supply of VAX-24 finished drug product. Under the Lonza Agreements, we are obligated to pay Lonza agreed-upon fees for Lonza’s performance of manufacturing services, and to reimburse Lonza for its out-of-pocket costs associated with purchasing raw materials, plus a customary handling fee. Each Lonza Agreement is managed by a steering committee and any dispute at the steering committee will be resolved by senior executives of the parties.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2021
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock	7. Redeemable Convertible Preferred Stock There were no shares of redeemable convertible preferred stock authorized or outstanding as of December 31, 2021. In connection with our IPO in June 2020, the outstanding shares of our Series A, Series B, Series C and Series D Redeemable Convertible Preferred Stock automatically converted into 28,610,337 shares of common stock.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Common Stock	8. Common Stock Our certificate of incorporation authorizes us to issue up to 500,000,000 shares of common stock with $ 0.001 par value per share, of which 53,031,978 and 51,071,593 shares were issued and outstanding as of December 31, 2021 and 2020, respectively. The holders of our common stock are also entitled to receive dividends whenever funds are legally available, when and if declared by our board of directors. As of December 31, 2021 and 2020, no dividends have been declared. Each share of common stock is entitled to one vote. In July 2021, we entered into an Open Market Sales Agreement SM (the “ATM Sales Agreement”) with Jefferies LLC (“Jefferies”), which provides that, upon the terms and subject to the conditions and limitations set forth in the ATM Sales Agreement, we may elect to issue and sell, from time to time, shares of our common stock having an aggregate offering price of up to $ 150.0 million through Jefferies acting as our sales agent or principal. We are obligated to pay Jefferies a commission of up to 3.0 % of the gross sales proceeds of any common stock sold through Jefferies under the ATM Sales Agreement; however, we are not obligated to make any sales of common stock. As of December 31, 2021 , we have sold 567,045 shares of our common stock under the ATM Sales Agreement at an average price of $ 25.26 per share for aggregate gross proceeds of $ 14.3 million ($ 13.9 million net of commissions and offering expenses). Common stock reserved for future issuances under the 2020 Equity Incentive Plan (the “2020 Plan”) and the 2014 Equity Incentive Plan (the “2014 Plan”) was as follows, and excludes 62,382 shares issued outside of the 2014 Plan and 2020 Plan: December 31, December 31, 2021 2020 Options issued and outstanding 5,295,007 5,188,531 Shares available for future stock option grants 6,104,756 4,651,149 Total 11,399,763 9,839,680

Warrants

Warrants	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Warrants	9. Warrants In connection with our IPO in June 2020, our outstanding warrants were automatically net exercised for an aggregate 46,869 shares of common stock.

Equity Incentive Plans

Equity Incentive Plans	12 Months Ended
	Dec. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	10. Equity Incentive Plans 2020 and 2014 Equity Incentive Plans In June 2020, our board of directors adopted, and our stockholders approved, the 2020 Plan, which became effective on June 11, 2020. Under the 2020 Plan, we may grant stock options, appreciation rights, restricted stock and restricted stock units to employees, consultants and directors. Stock options granted under the 2020 Plan may be either incentive stock options or nonqualified stock options. Incentive stock options may be granted only to our employees, including officers and directors who are also employees. Nonqualified stock options may be granted to our employees, officers, directors, consultants and advisors. The exercise price of stock options granted under the 2020 Plan must be at least equal to the fair market value of the common stock on the date of grant, except that an incentive stock option granted to an employee who owns more than 10 % of the shares of our common stock shall have an exercise price of no less than 110 % of the fair value per share on the grant date and expire five years from the date of grant. The maximum term of stock options granted under the 2020 Plan is 10 years, unless subject to the provisions regarding 10 % stockholders. Our stock options granted to new employees generally vest over four years at a rate of 25 % upon the first anniversary of the vesting commencement date and monthly thereafter. Our other stock options granted to employees generally vest monthly over four years from the vesting commencement date. A total of 10,150,000 shares of common stock were approved to be initially reserved for issuance under the 2020 Plan. The number of shares that remained available for issuance under the 2014 Plan as of the effective date of the 2020 Plan, and shares subject to outstanding awards under the 2014 Plan as of the effective date of the 2020 Plan that are subsequently canceled, forfeited or repurchased by us, will be added to the shares reserved under the 2020 Plan. In addition, the number of shares of common stock available for issuance under the 2020 Plan is automatically increased on the first day of each calendar year during the 10-year term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount equal to 5 % of the outstanding number of shares of our common stock on December 31 of the preceding calendar year or such lesser amount as determined by our board of directors. As of December 31, 2021, an aggregate of 6,104,756 shares of common stock were available for issuance under the 2020 Plan. Effective January 1, 2022, the number of shares of common stock available under the 2020 Plan increased by 2,651,598 shares pursuant to the evergreen provision of the 2020 Plan. Our 2014 Plan permitted the granting of incentive stock options, non-statutory stock options, restricted stock and other stock-based awards. Subsequent to the adoption of the 2020 Plan, no additional equity awards can be made under the 2014 Plan. Shares reserved and remaining available for issuance under the 2014 Plan were added to the 2020 Plan reserve upon its effectiveness. The terms of the 2014 Plan permit the exercise of options granted prior to vesting, subject to required approvals. The unvested shares are subject to our lapsing repurchase right upon termination of employment at the original purchase price. Shares purchased by employees pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be issued until those shares vest according to their respective vesting schedules. Cash received for early exercised stock options is recorded as other liabilities on the balance sheet and is reclassified to common stock and additional paid-in capital as such shares vest. As of December 31, 2021, 3,657,394 shares and 1,637,613 shares of common stock were subject to outstanding options under the 2014 Plan and 2020 Plan, respectively. At December 31, 2021 and 2020, 7,410 shares and 15,056 shares, respectively, remained subject to our right of repurchase as a result of the early exercised stock options. The remaining liabilities related to early exercised shares as of December 31, 2021 and 2020 were both less than $ 0.1 million and were recorded in other liabilities. Activity under our 2020 Plan and 2014 Plan, which excludes options to purchase 62,382 shares granted outside of the 2020 Plan and 2014 Plan, was as follows: Options Outstanding Stock Option Activity Options Number Weighted- Weighted- Aggregate Balances — December 31, 2019 835,941 3,297,586 $ 1.93 Additional shares authorized 5,997,435 — Options granted ( 2,255,690 ) 2,255,690 $ 8.93 Options exercised — ( 358,264 ) $ 1.88 Options forfeited 73,463 ( 73,463 ) $ 3.50 Balances — December 31, 2020 4,651,149 5,121,549 $ 4.99 Additional shares authorized 2,553,579 — Options granted ( 1,616,021 ) 1,616,021 $ 21.83 Options exercised — ( 926,514 ) $ 3.25 Options forfeited 516,049 ( 516,049 ) $ 16.70 Balances — December 31, 2021 6,104,756 5,295,007 $ 9.30 7.89 $ 78,604 Vested and expected to vest — December 31, 2021 5,295,007 $ 9.30 7.89 $ 78,604 Exercisable at December 31, 2021 2,611,523 $ 4.76 7.07 $ 50,123 During the years ended December 31, 2021 and 2020, 926,514 and 358,264 shares of stock options, respectively, were exercised for cash at a weighted-average price per share of $ 3.25 and $ 1.88 , respectively. The weighted-average grant date fair value of options granted for the years ended December 31, 2021 and 2020 was $ 14.65 and $ 9.62 , respectively. The intrinsic value of the stock options exercised was $ 18.9 million and $ 7.8 million for the years ended December 31, 2021 and 2020, respectively. 2020 Employee Stock Purchase Plan In June 2020, our board of directors adopted, and our stockholders approved, the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective on June 11, 2020. The 2020 ESPP permits participants to purchase common stock through payroll deductions of up to 15 % of their eligible compensation. Employees purchase shares of common stock at a price per share equal to 85 % of the lower of the fair market value at the start or end of the six-month purchase periods within the two-year offering period. A total of 650,000 shares of common stock were approved to be initially reserved for issuance under the 2020 ESPP. In addition, the number of shares of common stock available for issuance under the 2020 ESPP is automatically increased on the first day of each calendar year during the 10-year term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount of 1 % of the outstanding number of shares of our common stock on December 31 of the preceding calendar year or such lesser amount as determined by our board of directors. For the year ended December 31, 2021 , employees acquired 62,546 shares of our common stock under the 2020 ESPP and 1,070,704 shares of common stock remained available for issuance under the 2020 ESPP. Effective January 1, 2022, the number of shares of common stock available under the 2020 ESPP increased by 530,319 shares pursuant to the evergreen provision of the 2020 ESPP. Stock-based Compensation We estimated the fair value of employee stock options using the Black-Scholes option-pricing model for the years ended December 31, 2021, 2020 and 2019 using the following weighted-average assumptions: Year Ended December 31, 2021 2020 2019 Fair Value Assumptions Expected volatility 81.0 % - 84.1 % 81.2 % - 94.1 % 78.4 % - 80.4 % Expected dividend yield 0 % 0 % 0 % Expected term (in years) 5.3 - 5.5 5.6 - 6.1 5.9 - 6.1 Risk-free interest rate 0.5 % - 1.3 % 0.3 % - 1.4 % 1.6 % - 2.4 % We estimated the fair value of shares under the 2020 ESPP using the Black-Scholes option-pricing model for the years ended December 31, 2021, 2020 and 2019 using the following weighted-average assumptions: Year Ended December 31, 2021 2020 2019 Fair Value Assumptions Expected volatility 79.6 % - 126.3 % 105.8 % - 158.2 % N/A Expected dividend yield 0 % 0 % N/A Expected term (in years) 0.5 - 2.0 0.4 - 2.0 N/A Risk-free interest rate 0.0 % - 0.5 % 0.1 % - 0.2 % N/A We recorded total stock-based compensation expense for the years ended December 31, 2021, 2020 and 2019 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the statements of operations and allocated the amounts as follows: Year Ended December 31, 2021 2020 2019 (In thousands) Research and development $ 3,954 $ 1,861 $ 368 General and administrative 6,775 3,573 817 Total $ 10,729 $ 5,434 $ 1,185 Upon our IPO, 362,935 performance-based awards vested and, as a result, we recognized $ 0.3 million of stock-based compensation expense during the three months ended June 30, 2020, which amount is included in the above table for the year ended December 31, 2020. As of December 31, 2021, there was $ 27.5 million of unrecognized stock-based compensation expense related to the employee and non-employee awards, which is expected to be recognized over a weighted-average period of 2.5 years.

Funding Arrangement

Funding Arrangement	12 Months Ended
	Dec. 31, 2021
Funding Arrangement [Abstract]
Funding Arrangement	11. Funding Arrangement In July 2019, we received a cost-reimbursement research award from Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator (“CARB-X”), a public-private partnership funded under a Cooperative Agreement from Assistant Secretary for Preparedness and Response/Biomedical Advanced Research and Development Authority (“BARDA”) and by awards from Wellcome Trust, Germany’s Federal Ministry of Education and Research, the United Kingdom Global Antimicrobial Resistance Innovation Fund and the Bill & Melinda Gates Foundation. In connection with this funding, we entered into a cost-reimbursement sub-award agreement with the Trustees of Boston University, the administrator of the program. The initial award provided the potential for funding up to four years to develop a universal vaccine to prevent infections caused by Group A Strep bacteria, which include pharyngitis, impetigo and necrotizing fasciitis. The initial award committed initial funding of up to $ 1.6 million for our VAX-A1 program and, subject to a CARB-X decision to extend the options, up to $ 15.1 million in total funding available upon achievement of development milestones over the next four years . Specified research expenditures are reimbursable expenses associated with agreed-upon activities needed to advance the research project supported by the grant. These expenditures can include labor, laboratory supplies, travel, consulting and third-party vendor research and development support costs. In July 2020, the CARB-X agreement was amended with the initial funding amount increased from $ 1.6 million to $ 2.7 million. In December 2020, we reached the maximum CARB-X funding limit for this initial funding period, and subsequently submitted our funding proposal to CARB-X for the next period under our agreement. In April 2021, we received approval for the next phase of CARB-X development and executed the cost-reimbursement sub-award agreement with the Trustees of Boston University in August 2021. Pursuant to the agreement, the award committed additional funding of $ 3.2 million for IND-enabling activities and total potential funding of up to $ 29.7 million (including the current $ 3.2 million award and the prior $ 2.7 million award) upon the achievement of future VAX-A1 development milestones. In January 2022, CARB-X revised the parameters for the contribution of CARB-X funding and implemented maximum funding levels for all grant recipients. As a result, our total funding available upon achievement of development milestones through Phase 1 human clinical trials was revised from $ 29.7 million to $ 13.9 million. In April 2021, we received a cost-reimbursement research award from the National Institutes of Health (“NIH”). In connection with this funding, we entered into a cost-reimbursement sub-award agreement with the University of Maryland, Baltimore, the administrator of the program. The award provides for potential funding up to five years totaling approximately $ 0.5 million to develop a vaccine to prevent infections caused by Shigella. Income from grants is recognized in the period during which the related specified expenses are incurred, provided that the conditions under which the grants were provided have been met. We recognized $ 1.6 million, $ 2.5 million and $ 0.2 million of grant income and recorded the amounts in Other income (expense), net in the statement of operations during the years ended December 31, 2021, 2020, and 2019 respectively. A grant receivable of $ 1.2 million and $ 0.3 million representing unreimbursed, eligible costs incurred under the CARB-X agreement was recorded and included in Prepaid expenses and other current assets in the balance sheet as of December 31, 2021 and 2020, respectively.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	12. Net Loss Per Share The following table sets forth the computation of basic and diluted net loss per share and excludes shares which are legally outstanding, but subject to repurchase by us: Year Ended December 31, 2021 2020 2019 Net loss (in thousands) $ ( 100,077 ) $ ( 89,217 ) $ ( 50,274 ) Weighted-average shares outstanding used in computing net 51,922,108 29,545,810 3,795,090 Net loss per share, basic and diluted $ ( 1.93 ) $ ( 3.02 ) $ ( 13.25 ) The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the period presented because including them would have been antidilutive: Year Ended December 31, 2021 2020 2019 Stock options 5,357,389 5,188,531 3,364,568 Redeemable convertible preferred stock: Series A — — 6,225,719 Series B — — 6,786,896 Series C — — 7,377,480 Common stock warrant — — 31,857 Redeemable convertible preferred stock warrant — — 59,276 Total 5,357,389 5,188,531 23,845,796

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes Our pre-tax book loss was derived from our business operations within the United States. A reconciliation of our effective tax rate to the statutory U.S. federal rate is as follows: Year Ended December 31, 2021 2020 (1) 2019 (1) Statutory rate 21.0 % 21.0 % 21.0 % Stock-based compensation 2.2 % 0.8 % ( 0.4 )% Credits 1.1 % 0.6 % ( 0.5 )% Change in fair value of tranche liability 0.0 % 0.0 % 1.3 % Change in valuation allowance ( 23.0 )% ( 22.1 )% ( 21.8 )% Section 162(m) limitation ( 1.1 )% ( 0.1 )% 0.0 % Other ( 0.2 )% ( 0.2 )% 0.4 % Total 0.0 % 0.0 % 0.0 % (1) The 2019 and 2020 effective tax rate reconciliations have been updated to conform to the 2021 presentation. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of the assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The following table presents significant components of our deferred tax assets as of December 31, 2021 and 2020: As of December 31, 2021 2020 (in thousands) Deferred tax assets: Net operating losses 85,574 52,330 Fixed assets 1,700 528 Accruals & reserves 4,131 2,786 Credits 2,865 1,222 Section 59(e) capitalized expenses 2,984 3,381 Accrued manufacturing expenses 1,006 3,374 Lease liability 6,674 — Total deferred tax assets 104,934 63,621 Deferred tax liabilities: ROU asset ( 8,349 ) — Total deferred tax liabilities ( 8,349 ) — Net deferred tax asset 96,585 63,621 Valuation allowance ( 96,585 ) ( 63,621 ) Net deferred taxes $ — $ — At December 31, 2021, we have net operating loss carryforwards of approximately $ 296.7 million and $ 262.7 million available to reduce future taxable income, if any, for federal and state income tax purposes, respectively. The federal and state net operating loss carryforwards, except the federal loss carryforward arising in tax years beginning after December 31, 2017, begin to expire in 2034 unless previously utilized. Federal net operating losses arising in tax years beginning after December 31, 2017 have an indefinite carryover period and do not expire. At December 31, 2021, we have research credit carryforwards of $ 2.2 million and $ 1.6 million available to offset future income tax liabilities, if any, for federal and California income tax purposes, respectively. The federal research and development tax credit carryforwards expire beginning in 2039 unless previously utilized. The California tax credits can be carried forward indefinitely. We have evaluated the positive and negative evidence bearing upon the realizability of our deferred tax assets. Based on our history of operating losses, we have concluded that it is more likely than not that the benefit of our deferred tax assets will not be realized. Accordingly, we have provided a full valuation allowance for deferred tax assets as of December 31, 2021 and 2020. Utilization of the net operating loss carryforward and research credit carryforward may be subject to an annual limitation due to the ownership percentage change limitations under Section 382 and Section 383, respectively, provided by the Internal Revenue Code of 1986, as amended (the “Code”), and similar state provisions. The annual limitation may result in the expiration of the net operating loss before utilization. We have experienced ownership changes in the past. As a result of the ownership changes, we have determined that approximately less than $ 0.1 million of our federal research credits will expire unutilized, and such amounts are excluded from our research credit carryforwards. The Company does not expect any ownership changes during the year ended December 31, 2021 to result in a limitation that would materially reduce the total amount of net operating loss carryforwards and credits that can be utilized. Subsequent ownership changes may affect the limitation in future years. We have uncertain tax benefits (“UTBs”) totaling $ 0.9 million and $ 0.4 million as of December 31, 2021 and 2020, respectively, which were netted against deferred tax assets subject to valuation allowance. The UTBs had no effect on the effective tax rate. We recognize interest and penalties related to UTBs, when they occur, as a component of income tax expense. To the extent accrued interest and penalties do not ultimately become payable, amounts accrued will be reduced and reflected as a reduction of the provision for income taxes in the period such determination is made. There were no interest or penalties recognized for the years ended December 31, 2021 and 2020. We do not expect our UTBs to change significantly over the next 12 months. A reconciliation of the beginning and ending unrecognized tax benefit amount is as follows: December 31, 2021 2020 2019 (in thousands) Balance at the beginning of the year $ 393 $ 271 $ 408 Additions based on tax positions related to current year 461 287 217 Adjustments based on tax positions related to prior years 70 ( 165 ) ( 354 ) Balance at end of year $ 924 $ 393 $ 271 We file U.S. federal and state tax returns. In general, the Company is no longer subject to tax examination by the Internal Revenue Service or state taxing authorities for years before 2016. Although the federal and state statutes are closed for purposes of assessing additional income tax in those prior years, the taxing authorities may still make adjustments to the net operating loss, or NOL, and credit carryforwards used in open years. Therefore, the tax statutes should be considered open as it relates to the NOL and credit carryforwards used in open years. We do not have any tax audits or other issues pending. On March 27, 2020, the President of the United States signed into law the Coronavirus Aid, Relief, and Economic Security Act (CARES Act). The CARES Act, among other things, includes certain income tax provisions for individuals and corporations; however, these benefits do not impact our current tax provision. On December 21, 2020, the President of the United States signed into law the “Consolidated Appropriations Act, 2021” which includes further COVID-19 economic relief and extension of certain expiring tax provisions. The relief package includes a tax provision clarifying that businesses with forgiven Paycheck Protection Program, or PPP, loans can deduct regular business expenses that are paid for with the loan proceeds. Additional pandemic relief tax measures include an expansion of the employee retention credit, enhanced charitable contribution deductions and a temporary full deduction for business expenses for food and beverages provided by a restaurant. These benefits do not have a material impact on the current tax provision.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	14. Related Party Transactions We have an ongoing relationship with Sutro Biopharma. In 2013, Sutro Biopharma provided support to facilitate the establishment of our Company. As of December 31, 2021 and 2020, Sutro Biopharma owned approximately 1.6 million shares of our common stock. As of December 31, 2019, Sutro Biopharma also owned warrants to purchase 31,857 shares of our common stock (the “Common Stock Warrant”) at an exercise price of $ 0.79289 per share and 59,276 shares of our Series C redeemable convertible stock (the “Preferred Stock Warrant”) at an exercise price of $ 11.5215 per share. The Common Stock Warrant and the Preferred Stock Warrant were automatically net exercised pursuant to their terms for 30,278 shares and 16,591 shares, respectively, of our common stock in connection with the IPO. In the agreements and amendments identified herein, we licensed certain intellectual property and acquired certain supply rights from Sutro Biopharma, including the right to use the XpressCF platform to discover and develop vaccine candidates for the treatment or prophylaxis of infectious diseases. On October 12, 2015, we and Sutro Biopharma (“the Parties”) entered into the Sutro Biopharma License Agreement, which amended and restated an agreement dated August 1, 2014. The Sutro Biopharma License Agreement was subsequently amended on May 9, 2018 (“License Amendment A1”) and May 29, 2018 (“License Amendment A2”). In consideration for the License Amendment A2, we issued to Sutro Biopharma the Preferred Stock Warrant to purchase 59,276 shares of Series C redeemable convertible preferred stock at a purchase price of $ 11.5215 per share. We also entered into a separate supply agreement with Sutro Biopharma on May 29, 2018 (the “Sutro Biopharma Supply Agreement”). As of June 2, 2021, Sutro Biopharma was no longer considered a related party. Under the Sutro Biopharma License Agreement, Sutro Biopharma granted us an exclusive, worldwide license to research, develop, manufacture and commercialize vaccine products addressing infectious disease, which are discovered or produced based on the use of Sutro Biopharma’s proprietary cell-free protein expression technology, known as XpressCF, which utilizes extracts derived from strains of E. coli . In connection with the Sutro Biopharma License Agreement, under the Sutro Biopharma Supply Agreement, Sutro Biopharma has agreed to manufacture and supply extracts and reagents for us on a cost-plus basis. In consideration for the rights licensed, we are obligated to pay a 4 % royalty on worldwide aggregate annual net sales of our vaccine products for human health and a 2 % royalty on annual net sales of vaccine products for animal health. In License Amendment A1, the Parties amended the license agreement to remove a pre-IND regulatory meeting as a diligence milestone and to agree that certain other diligence milestones had been satisfied. In License Amendment A2, the Parties amended the license agreement to add certain terms confirming our obligation to purchase Sutro Biopharma’s proprietary extract from E. coli (“Extract”) from Sutro Biopharma. In addition, the Parties amended the license agreement to specify our rights to a transfer of certain know-how relating to the manufacture of Extract in the event of a declaration of bankruptcy by Sutro Biopharma. Finally, the Parties agreed to terms providing for injunctive relief in the event of a breach or threatened breach by the other party. In the Sutro Biopharma Supply Agreement, the Parties agreed to terms for the supply of manufactured Extract and custom reagents by Sutro Biopharma for us to use in manufacturing vaccine compositions in non-clinical research or in Phase 1 or Phase 2 clinical trials. The term of the Sutro Biopharma Supply Agreement is from execution until the later of July 31, 2021 and the date the parties enter into and commence activities under the supply agreement unless extended through a subsequent supply agreement for the supply of Extract and custom reagents for vaccine compositions for Phase 3 and commercial uses as contemplated in the Supply Agreement. In February 2021, we entered into an amendment to the Sutro Biopharma Supply Agreement and extended the term to July 31, 2022. We recognized expense related to the Supply Agreement of $ 2.4 million, $ 1.2 million and $ 1.1 million for the years ended December 31, 2021, 2020 and 2019, respectively. In addition, we recorded $ 0 , $ 0.2 million and $ 0 in changes in the fair value of the Preferred Stock Warrant for the years ended December 31, 2021, 2020 and 2019, respectively. The expense related to the changes in the fair value of the warrant is included in research and development expenses in the statements of operations. Accrued expenses payable to Sutro Biopharma were $ 0 and $ 0.7 million as of December 31, 2021 and 2020, respectively.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events In January 2022, we completed an underwritten public offering in which we issued 2,500,000 shares of our common stock at a price of $ 20.00 per share, and pre-funded warrants to purchase 2,500,000 shares of our common stock at a price of $ 19.999 per underlying share. We received approximately $ 93.5 million in net proceeds after deducting underwriting discounts and commissions and other estimated offering expenses payable by us. In February 2022, t he underwriters exercised their option to purchase an additional 750,000 shares of common stock, and we received approximately $ 14.1 million in additional net proceeds after deducting underwriting discounts and commissions.

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding annual reporting. Certain changes in presentation were made in these financial statements as of and for the year ended December 31, 2019 to conform to the presentation as of and for the years ended December 31, 2021 and 2020.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities at the date of the financial statements. On an ongoing basis, we evaluate our estimates and assumptions, including those related to stock-based compensation expense, accruals for certain research and development costs, the incremental borrowing rate, the valuation of deferred tax assets and income taxes. Management bases our estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject us to a concentration of credit risk consist primarily of cash and cash equivalents and investments. We invest in money market funds, U.S. Treasury securities, U.S. government agency securities, corporate debt, commercial paper and asset-backed securities. We maintain bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. We are exposed to credit risk in the event of a default by the financial institutions holding our cash and issuers of investments to the extent recorded on the balance sheets. Our investment policy limits investments to money market funds, certain types of debt securities issued by the U.S. Government and its agencies, corporate debt, commercial paper and asset-backed securities, and places restrictions on the credit ratings, maturities and concentration by type and issuer. We have not experienced any significant losses on our deposits of cash, cash equivalents or investments. We are subject to supplier concentration risk from our suppliers. We source our critical raw materials from a sole source supplier, Sutro Biopharma, Inc. (“Sutro Biopharma”). We also use one contract manufacturing organization (“CMO”), Lonza Ltd. (“Lonza”), to handle most of our manufacturing activities. If we were to experience disruptions in raw materials supplied by Sutro Biopharma, or in manufacturing activities at Lonza, we may experience significant delays in our product development timelines and may incur substantial costs to secure alternative sources of raw materials or manufacturing. Our future results of operations involve a number of other risks and uncertainties. Factors that could affect our future operating results and cause actual results to vary materially from expectations include, but are not limited to: our early stages of clinical vaccine development; our ability to advance vaccine candidates into, and successfully complete, clinical trials on the timelines we project; our ability to adequately demonstrate sufficient safety and efficacy of our vaccine candidates; our ability to enroll subjects in our ongoing and future clinical trials; our ability to successfully manufacture and supply our vaccine candidates for clinical trials; our ability to obtain additional capital to finance our operations; our ability to obtain, maintain and protect our intellectual property rights; developments relating to our competitors and our industry, including competing vaccine candidates; general and market conditions; and other risks and uncertainties, including those more fully described in the “Risk Factors” section of this Annual Report on Form 10-K.
Segment and Geographical Information	Segment and Geographical Information We operate and manage our business as one reportable and operating segment. Our chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. All of our long-lived assets are based in the United States. Long-lived assets are comprised of property and equipment.
Cash and Cash Equivalents	Cash, Cash Equivalents and Restricted Cash We consider all highly liquid investments purchased with original maturities of three months or less from the date of purchase to be cash and cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and commercial paper and are stated at their fair values. Restricted cash consists of a standby letter of credit, which was issued in the first quarter of 2021, that serves as collateral for the lease agreement for our new corporate headquarters. Cash, cash equivalents and restricted cash as reported within the statement of cash flows consisted of the following: Years Ended December 31, 2021 2020 2019 (in thousands) Cash and cash equivalents $ 68,985 $ 386,200 $ 58,976 Restricted cash 871 — — Cash, cash equivalents and restricted cash $ 69,856 $ 386,200 $ 58,976
Investments	Investments Our investments have been classified and accounted for as available-for-sale securities. Our investments consist of U.S. Treasury securities, U.S. government agency securities, corporate debt, commercial paper and asset-backed securities. These securities are recorded on the balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive loss. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income (expense), net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income (expense), net. We evaluate securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are included in other income (expense), net. We classify our investments as short or long term primarily based on the remaining contractual maturity of the securities.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs consist of fees and expenses incurred in connection with the sale of our common stock in equity transactions, including legal, accounting, printing and other issuance-related costs. Prior to the completion of equity transactions, deferred offering costs are included in Other assets on the balance sheet. In connection with and as of the closing of equity transactions, these costs are reclassified to Additional paid-in capital, representing a reduction to the gross proceeds. As of December 31, 2020, $ 3.4 million of IPO-related costs were included in the Additional paid-in capital line item on the balance sheet. As of December 31, 2021 and 2020, $ 0.5 million and $ 0.1 million of deferred offering costs, respectively, were included in Other assets on the balance sheet.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally three to five years . Leasehold improvements are amortized over the shorter of the expected life or lease term. Repairs and maintenance expenditures, which are not considered improvements and do not extend the useful life of property and equipment, are expensed as incurred. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is reflected in the statements of operations in the period realized.
Leases	Leases Under Financial Accounting Standards Board (FASB) Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) and its associated amendments (“ASC 842”), we determine if an arrangement is a lease at inception. In addition, we determine whether a lease meets the classification criteria of a finance or operating lease at the lease commencement date considering whether: (i) the lease transfers ownership of the underlying asset to the lessee at the end of the lease term; (ii) the lease grants the lessee an option to purchase the underlying asset that the lessee is reasonably certain to exercise; (iii) the lease term is for a major part of the remaining economic life of the underlying asset; (iv) the present value of the sum of the lease payments and residual value guaranteed by the lessee equals or exceeds substantially all of the fair value of the underlying asset; and (v) the underlying asset is such a specialized nature that it is expected to have no alternative use to the lessor at the end of the lease term. As of December 31, 2021, our lease population consisted of real estate operating leases. As of December 31, 2021 , we did no t have any finance leases. Operating leases are included in Operating lease right-of-use (ROU) assets, Operating lease liabilities — current and Operating lease liabilities — long term in our balance sheet. ROU assets represent our right to use the underlying assets for the lease term and lease liabilities represent our obligation to make lease payments arising from the leases. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, if the rate implicit in the lease is not readily determinable, we use our incremental borrowing rate based on the information available at the lease commencement date. We determine the incremental borrowing rate based on an analysis of corporate bond yields with a credit rating similar to us. The determination of our incremental borrowing rate requires management judgment, including development of a synthetic credit rating and cost of debt, as we currently do not carry any debt. We believe that the estimates used in determining the incremental borrowing rate are reasonable based upon current facts and circumstances. Applying different judgment to the same facts and circumstances could yield a different incremental borrowing rate. The operating lease ROU assets also include adjustments for prepayments and accrued lease payments and exclude lease incentives. ROU assets and lease liabilities may include options to extend or terminate leases if it is reasonably certain that we will exercise such options. Lease payments which are fixed and determinable are amortized as rent and lease expense on a straight-line basis over the expected lease term. Variable lease costs, which are dependent on usage, a rate or index, including common area maintenance charges, are expensed as incurred. Lease agreements that include lease and non-lease components are accounted for as a single lease component. Lease agreements with non-cancelable terms of less than 12 months are not recorded on our balance sheets.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We review long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparing the carrying amount to the future undiscounted net cash flows which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows generated by the assets. There were $ 0 , $ 0.3 million, and $ 0 of impairments of long-lived assets during the years ended December 31, 2021, 2020 and 2019, respectively.
Fair Value Measurements	Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of our financial instruments, including cash and cash equivalents, prepaid and other current assets, accounts payable, accrued expenses, and other liabilities, approximate fair value due to their short-term maturities. Prior to their automatic conversion upon our IPO in June 2020, the redeemable convertible preferred stock tranche liability and redeemable convertible preferred stock warrant were carried at fair value (see Note 3).
Research and Development	Research and Development Research and development costs are expensed as incurred. Research and development costs include salaries, stock-based compensation and benefits for employees performing research and development activities, an allocation of facility and overhead expenses, expenses incurred under agreements with consultants, CMOs, contract research organizations (“CROs”) and investigative sites that conduct preclinical studies, other supplies and costs associated with product development efforts, preclinical activities and regulatory operations.
Accrued Research and Development	Accrued Research and Development We have entered into various agreements with CROs and CMOs. Our research and development accruals, which include accrued manufacturing expenses, are estimated based on the level of services performed, progress of the studies, including the phase or completion of events, and contracted costs. The estimated costs of research and development services provided, but not yet invoiced, are included in accrued expenses on the balance sheet. If the actual timing of the performance of services or the level of effort varies from the original estimates, we will adjust the accrual accordingly. Payments made to CROs or CMOs under these arrangements in advance of the performance of the related services are recorded as prepaid expenses and other current assets until the services are rendered. To date, there have been no material differences between our estimates of such expenses and the amounts actually incurred.
Income Taxes	Income Taxes We account for income taxes using the asset and liability method. We recognize deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover our deferred income tax assets, we consider all available positive and negative evidence, including our operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event we determine that we would be able to realize our deferred income tax assets in the future in excess of their net recorded amount, we would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2021 and 2020, we have recorded a full valuation allowance on our deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained during an audit. Interest and penalties related to unrecognized tax benefits are included within the provision for income tax.
Stock-Based Compensation Expense	Stock-Based Compensation Expense For options granted to employees, non-employees, and directors, stock-based compensation is measured at grant date based on the fair value of the award. We determine the grant-date fair value of the options using the Black-Scholes option-pricing model. The grant-date fair value of awards is amortized over the employees’ requisite service period or the non-employees’ vesting period as the services are rendered. Forfeitures are accounted for as they occur. Additionally, our 2020 Employee Stock Purchase Plan is deemed to be a compensatory plan and is therefore included in stock-based compensation expense.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and other comprehensive loss for the period. Other comprehensive loss consists of unrealized loss on investments.
Foreign Currency Transactions	Foreign Currency Transactions Transactions denominated in foreign currencies are initially measured in U.S. dollars using the exchange rate on the date of the transaction. Foreign currency denominated monetary assets and liabilities are subsequently re-measured at the end of each reporting period using the exchange rate at that date, with the corresponding foreign currency transaction gain or loss recorded in the statements of operations and statements of cash flows. Nonmonetary assets and liabilities are not subsequently re-measured.
Net Loss Per Share	Net Loss Per Share Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common stock outstanding during the period, without consideration of potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, redeemable convertible preferred stock, redeemable convertible preferred stock warrant, common stock subject to repurchase, and stock options are considered to be potentially dilutive securities. Basic and diluted net loss attributable to common stockholders per share is presented in conformity with the two-class method required for participating securities as the redeemable convertible preferred stock is considered a participating security. Our participating securities do not have a contractual obligation to share in our losses. As such, the net loss was attributed entirely to common stockholders. Because we have reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . ASU 2016-02 was subsequently amended by ASU 2018-01, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2019-10 and ASU 2020-05, which the FASB issued in January 2018, July 2018, July 2018, December 2018, March 2019, November 2019 and June 2020, respectively (collectively, “ASC 842”). ASC 842 requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new standard establishes a ROU model that requires a lessee to recognize a ROU asset and a lease liability on the balance sheet for all leases with a term longer than 12 months. Under ASC 842, leases are classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement. We early adopted the new standard effective January 1, 2021 using the modified retrospective transition approach. Upon adoption on January 1, 2021, we recognized ROU assets and lease liabilities totaling $ 0.9 million and $ 0.9 million, respectively, to reflect the present value of remaining lease payments under existing lease arrangements. The difference between the leased assets and lease liabilities represents the existing deferred rent liabilities balance resulting from historical straight-lining of operating leases for our facilities, which was reclassified upon adoption to reduce the measurement of the leased assets. The balance of our deferred rent liabilities, which was reclassified to reduce the ROU assets upon adoption, was immaterial . We applied the modified retrospective transition approach and did not recast prior periods. Although we applied this approach, we did not have a cumulative effect adjustment to the opening balance of our retained deficit upon adoption. As permitted by the standard, we elected the transition practical expedient package, which among other things, allowed the carryforward of historical lease classifications. For additional details regarding the impact of adoption and disclosure, see Note 5, “Leases, " to our financial statements included in Part II, Item 8 of this Annual Report on Form 10-K. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740) . The amendments in ASU 2019-12 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify U.S. GAAP or other areas of Topic 740 by clarifying and amending existing guidance. The new standard was effective for us on January 1, 2021 and for interim periods within 2021. The adoption of ASU 2019-12 did not have a material impact on our financial statements. Recently Issued Accounting Pronouncements—Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments and has subsequently issued related amendments, collectively referred to as “Topic 326.” Topic 326 requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. We are currently assessing the impact of this standard to our financial statements and related disclosures. In November 2021, the FASB issued ASU 2021-10, Government Assistance (Topic 832): Disclosure by Business Entities about Government Assistance, which requires disclosures about transactions with a government entity that are accounted for by applying a grant or contribution accounting model by analogy to other accounting guidance, such as a grant model within International Accounting Standard 20, Accounting for Government Grants and Disclosure of Government Assistance , or Subtopic 958-605, Not-For-Profit Entities - Revenue Recognition . The required disclosures include (i) the nature of the transactions and the related accounting policy used to account for the transactions, (ii) the financial statement line items that are affected by the transactions and (iii) the significant terms and conditions of the transactions, including commitments and contingencies. This standard is effective for annual periods beginning after December 15, 2021, with early adoption and retrospective or prospective application permitted. This standard is effective for us on January 1, 2022 and only impacts annual financial statement footnote disclosures . In Note 11, "Funding Arrangement," to our financial statements included in Part II, Item 8 of this Annual Report on Form 10-K, we included disclosures on our cost-reimbursement research award from CARB-X. Therefore, we do not believe the adoption of this standard will have a material impact on our financial statements.

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Schedule of Cash, Cash Equivalents And Restricted Cash	Cash, cash equivalents and restricted cash as reported within the statement of cash flows consisted of the following: Years Ended December 31, 2021 2020 2019 (in thousands) Cash and cash equivalents $ 68,985 $ 386,200 $ 58,976 Restricted cash 871 — — Cash, cash equivalents and restricted cash $ 69,856 $ 386,200 $ 58,976

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Financial Instruments Measured at Fair Value on Recurring Basis	The following tables set forth our financial instruments measured at fair value on a recurring basis by level within the fair value hierarchy at December 31, 2021 and 2020: December 31, 2021 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 27,834 $ — $ — $ 27,834 Money market funds Level 1 17,555 — — 17,555 Commercial paper Level 2 23,597 — ( 1 ) 23,596 Total cash and cash equivalents $ 68,986 $ — $ ( 1 ) $ 68,985 Investments: U.S. Treasury securities Level 1 45,290 — ( 73 ) 45,217 Commercial paper Level 2 61,941 — ( 22 ) 61,919 Corporate debt Level 2 58,498 — ( 74 ) 58,424 Asset backed securities Level 2 13,899 ( 25 ) 13,874 U.S. government agency securities Level 2 24,714 — ( 46 ) 24,668 Total investments 204,342 — ( 240 ) 204,102 Total assets measured at fair value $ 273,328 $ — $ ( 241 ) $ 273,087 December 31, 2020 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 4,788 $ — $ — $ 4,788 Money market funds Level 1 381,412 — — 381,412 Total assets measured at fair value $ 386,200 $ — $ — $ 386,200
Schedule of Contractual Maturities of Investments	The following table presents the contractual maturities of our investments as of December 31, 2021 (in thousands): December 31, 2021 Fair Value Due in less than one year $ 176,985 Due in one to five years 27,117 Total $ 204,102

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	12 Months Ended
	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net as of December 31, 2021 and 2020 consisted of the following: December 31, 2021 2020 (in thousands) Furniture and equipment $ 1,619 $ 397 Computers and computer software 430 111 Lab equipment 9,453 4,739 Leasehold improvements — 1,903 Construction in progress — 219 Total property and equipment 11,502 7,369 Less: accumulated depreciation and amortization ( 3,548 ) ( 4,097 ) Property and equipment, net $ 7,954 $ 3,272
Schedule of Accrued Expenses	Accrued expenses as of December 31, 2021 and 2020 consisted of the following: December 31, 2021 2020 (in thousands) Preclinical studies $ 5,039 $ 2,844 Professional fees 400 490 Other accrued expenses 3,348 432 Total $ 8,787 $ 3,766

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Schedule of Information Related to ROU Assets and Lease Liabilities	Information related to our ROU assets and related lease liabilities was as follows (dollar amounts in thousands): December 31, 2021 Cash paid for operating lease liabilities $ 924 Right-of-use assets recognized in exchange for new lease obligations $ 27,958 Current operating lease liabilities $ 5,276 Non-current operating lease liabilities 11,507 Total lease liabilities $ 16,783 Weighted-average remaining lease term (in years) 3.75 Weighted-average discount rate 7.5 %
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities as of December 31, 2021 were as follows: Years ending December 31, (in thousands) 2022 (1) $ ( 105 ) 2023 6,639 2024 6,805 2025 6,976 Thereafter — Total future undiscounted lease payments 20,315 Less: Imputed interest ( 3,532 ) Total lease liabilities $ 16,783 _____________________________________________ (1) Maturities for 2022 are net of lease incentives of $ 0.9 million allocated to the Palo Alto office. Future minimum payments required under operating leases as of December 31, 2020 were as follows: Years ending December 31, (in thousands) 2021 $ 742 2022 190 Total future minimum payments $ 932

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Schedule of Common Stock Shares Reserved for Future Issuance	Common stock reserved for future issuances under the 2020 Equity Incentive Plan (the “2020 Plan”) and the 2014 Equity Incentive Plan (the “2014 Plan”) was as follows, and excludes 62,382 shares issued outside of the 2014 Plan and 2020 Plan: December 31, December 31, 2021 2020 Options issued and outstanding 5,295,007 5,188,531 Shares available for future stock option grants 6,104,756 4,651,149 Total 11,399,763 9,839,680

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2021
Summary of Estimated Fair Value of Employee Stock Options	We estimated the fair value of employee stock options using the Black-Scholes option-pricing model for the years ended December 31, 2021, 2020 and 2019 using the following weighted-average assumptions: Year Ended December 31, 2021 2020 2019 Fair Value Assumptions Expected volatility 81.0 % - 84.1 % 81.2 % - 94.1 % 78.4 % - 80.4 % Expected dividend yield 0 % 0 % 0 % Expected term (in years) 5.3 - 5.5 5.6 - 6.1 5.9 - 6.1 Risk-free interest rate 0.5 % - 1.3 % 0.3 % - 1.4 % 1.6 % - 2.4 %
2020 Plan and 2014 Plan
Summary of Activity Under Stock Option Plans	Activity under our 2020 Plan and 2014 Plan, which excludes options to purchase 62,382 shares granted outside of the 2020 Plan and 2014 Plan, was as follows: Options Outstanding Stock Option Activity Options Number Weighted- Weighted- Aggregate Balances — December 31, 2019 835,941 3,297,586 $ 1.93 Additional shares authorized 5,997,435 — Options granted ( 2,255,690 ) 2,255,690 $ 8.93 Options exercised — ( 358,264 ) $ 1.88 Options forfeited 73,463 ( 73,463 ) $ 3.50 Balances — December 31, 2020 4,651,149 5,121,549 $ 4.99 Additional shares authorized 2,553,579 — Options granted ( 1,616,021 ) 1,616,021 $ 21.83 Options exercised — ( 926,514 ) $ 3.25 Options forfeited 516,049 ( 516,049 ) $ 16.70 Balances — December 31, 2021 6,104,756 5,295,007 $ 9.30 7.89 $ 78,604 Vested and expected to vest — December 31, 2021 5,295,007 $ 9.30 7.89 $ 78,604 Exercisable at December 31, 2021 2,611,523 $ 4.76 7.07 $ 50,123
2020 Employee Stock Purchase Plan
Summary of Estimated Fair Value of Shares Under Employee Stock Purchase Plan	We estimated the fair value of shares under the 2020 ESPP using the Black-Scholes option-pricing model for the years ended December 31, 2021, 2020 and 2019 using the following weighted-average assumptions: Year Ended December 31, 2021 2020 2019 Fair Value Assumptions Expected volatility 79.6 % - 126.3 % 105.8 % - 158.2 % N/A Expected dividend yield 0 % 0 % N/A Expected term (in years) 0.5 - 2.0 0.4 - 2.0 N/A Risk-free interest rate 0.0 % - 0.5 % 0.1 % - 0.2 % N/A
2014 Plan, 2020 Plan and 2020 ESPP
Summary of Stock-based Compensation Expense	We recorded total stock-based compensation expense for the years ended December 31, 2021, 2020 and 2019 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the statements of operations and allocated the amounts as follows: Year Ended December 31, 2021 2020 2019 (In thousands) Research and development $ 3,954 $ 1,861 $ 368 General and administrative 6,775 3,573 817 Total $ 10,729 $ 5,434 $ 1,185

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Loss Per Share	The following table sets forth the computation of basic and diluted net loss per share and excludes shares which are legally outstanding, but subject to repurchase by us: Year Ended December 31, 2021 2020 2019 Net loss (in thousands) $ ( 100,077 ) $ ( 89,217 ) $ ( 50,274 ) Weighted-average shares outstanding used in computing net 51,922,108 29,545,810 3,795,090 Net loss per share, basic and diluted $ ( 1.93 ) $ ( 3.02 ) $ ( 13.25 )
Schedule of Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share	The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the period presented because including them would have been antidilutive: Year Ended December 31, 2021 2020 2019 Stock options 5,357,389 5,188,531 3,364,568 Redeemable convertible preferred stock: Series A — — 6,225,719 Series B — — 6,786,896 Series C — — 7,377,480 Common stock warrant — — 31,857 Redeemable convertible preferred stock warrant — — 59,276 Total 5,357,389 5,188,531 23,845,796

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Reconciliation of Effective Tax Rate	A reconciliation of our effective tax rate to the statutory U.S. federal rate is as follows: Year Ended December 31, 2021 2020 (1) 2019 (1) Statutory rate 21.0 % 21.0 % 21.0 % Stock-based compensation 2.2 % 0.8 % ( 0.4 )% Credits 1.1 % 0.6 % ( 0.5 )% Change in fair value of tranche liability 0.0 % 0.0 % 1.3 % Change in valuation allowance ( 23.0 )% ( 22.1 )% ( 21.8 )% Section 162(m) limitation ( 1.1 )% ( 0.1 )% 0.0 % Other ( 0.2 )% ( 0.2 )% 0.4 % Total 0.0 % 0.0 % 0.0 % (1) The 2019 and 2020 effective tax rate reconciliations have been updated to conform to the 2021 presentation.
Components of Deferred Tax Assets	The following table presents significant components of our deferred tax assets as of December 31, 2021 and 2020: As of December 31, 2021 2020 (in thousands) Deferred tax assets: Net operating losses 85,574 52,330 Fixed assets 1,700 528 Accruals & reserves 4,131 2,786 Credits 2,865 1,222 Section 59(e) capitalized expenses 2,984 3,381 Accrued manufacturing expenses 1,006 3,374 Lease liability 6,674 — Total deferred tax assets 104,934 63,621 Deferred tax liabilities: ROU asset ( 8,349 ) — Total deferred tax liabilities ( 8,349 ) — Net deferred tax asset 96,585 63,621 Valuation allowance ( 96,585 ) ( 63,621 ) Net deferred taxes $ — $ —
Reconciliation of Unrecognized Tax Benefit	A reconciliation of the beginning and ending unrecognized tax benefit amount is as follows: December 31, 2021 2020 2019 (in thousands) Balance at the beginning of the year $ 393 $ 271 $ 408 Additions based on tax positions related to current year 461 287 217 Adjustments based on tax positions related to prior years 70 ( 165 ) ( 354 ) Balance at end of year $ 924 $ 393 $ 271

Company Organization and Natu_2

Company Organization and Nature of Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Jun. 15, 2020shares	Jun. 05, 2020	Jun. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)shares	Jun. 17, 2020shares
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Reverse stock split		one-for-1.6870
Reverse stock split, conversion ratio		0.593
Net proceeds from initial public offering | $			$ 264,000
Underwriting discounts and commissions | $			20,100
Offering expenses | $			$ 3,400		$ 3,368
Redeemable Convertible Preferred Stock
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Conversion of preferred stock (in shares)			28,610,337
Redeemable convertible preferred stock, shares outstanding				0		0
Common Stock
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Conversion of preferred stock (in shares)	28,610,337				28,610,337
Initial Public Offering
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock shares sold			17,968,750
Underwriters' option to purchase additional shares			2,343,750
Public offering price per share | $ / shares			$ 16
Initial Public Offering | Common Stock
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Common stock shares sold					17,968,750
Pneumococcal Conjugate Vaccine
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Global target revenue | $				$ 7,000,000

Basis of Presentation and Sum_4

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)SegmentLease	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Jan. 01, 2021USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Number of reportable segments | Segment	1
Number of operating segments | Segment	1
Number of finance lease | Lease	0
Asset impairment charges	$ 0	$ 267	$ 0
ROU assets	27,958			$ 900
Lease liabilities	$ 16,783			900
Minimum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Estimated useful lives of assets	3 years
Maximum
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Estimated useful lives of assets	5 years
ASU 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, early adoption [true false]	true
Accounting standard update adoption date	Jan. 1, 2021
Accounting standard update material impact	true
ROU assets				900
Lease liabilities				$ 900
ASU 2019-12
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounting standard update adopted	true
Accounting standard update adoption date	Jan. 1, 2021
Accounting standard update material impact	true
Additional Paid-in Capital
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
IPO-related costs		3,400
Other Assets
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred offering costs	$ 500	$ 100

Basis of Presentation and Sum_5

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Cash, Cash Equivalents And Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 68,985	$ 386,200	$ 58,976
Restricted Cash	871
Cash, cash equivalents and restricted cash	$ 69,856	$ 386,200	$ 58,976	$ 66,090

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021USD ($)Security	Dec. 31, 2020USD ($)Security
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value assets transferred from level 1 to level 2	$ 0	$ 0
Fair value assets transferred from level 2 to level 1	0	0
Fair value liabilities transferred from level 1 to level 2	0	0
Fair value liabilities transferred from level 2 to level 1	0	0
Fair value assets transferred into level 3	0	0
Fair value assets transferred out of level 3	0	0
Fair value liabilities transferred into level 3	0	0
Fair value liabilities transferred out of level 3	$ 0	$ 0
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Number of securities | Security	0	0

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Assets:
Investments, Fair Value	$ 204,102
Fair Value, Recurring
Assets:
Cash and cash equivalents, Amortized Cost	68,986
Cash and cash equivalents, Gross Unrealized Losses	(1)
Cash and cash equivalents, Fair Value	68,985
Investments, Amortized Cost	204,342
Investments, Gross Unrealized Losses	(240)
Investments, Fair Value	204,102
Total assets measured at fair value, Amortized Cost	273,328	$ 386,200
Total assets measured at fair value, Gross Unrealized Losses	(241)
Total assets measured at fair value, Fair Value	273,087	386,200
Fair Value, Recurring | Cash | Level 1
Assets:
Cash and cash equivalents, Amortized Cost	27,834	4,788
Cash and cash equivalents, Fair Value	27,834	4,788
Fair Value, Recurring | Money Market Funds | Level 1
Assets:
Cash and cash equivalents, Amortized Cost	17,555	381,412
Cash and cash equivalents, Fair Value	17,555	$ 381,412
Fair Value, Recurring | Commercial Paper | Level 2
Assets:
Cash and cash equivalents, Amortized Cost	23,597
Cash and cash equivalents, Gross Unrealized Losses	(1)
Cash and cash equivalents, Fair Value	23,596
Fair Value, Recurring | U.S. Treasury Securities | Level 1
Assets:
Investments, Amortized Cost	45,290
Investments, Gross Unrealized Losses	(73)
Investments, Fair Value	45,217
Fair Value, Recurring | Commercial paper | Level 2
Assets:
Investments, Amortized Cost	61,941
Investments, Gross Unrealized Losses	(22)
Investments, Fair Value	61,919
Fair Value, Recurring | Corporate Debt | Level 2
Assets:
Investments, Amortized Cost	58,498
Investments, Gross Unrealized Losses	(74)
Investments, Fair Value	58,424
Fair Value, Recurring | Asset backed securities | Level 2
Assets:
Investments, Amortized Cost	13,899
Investments, Gross Unrealized Losses	(25)
Investments, Fair Value	13,874
Fair Value, Recurring | U.S. Government Agency Securities | Level 2
Assets:
Investments, Amortized Cost	24,714
Investments, Gross Unrealized Losses	(46)
Investments, Fair Value	$ 24,668

Fair Value Measurements and F_5

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Contractual Maturities of Investments (Details) $ in Thousands	Dec. 31, 2021USD ($)
Fair Value Disclosures [Abstract]
Due in less than one year	$ 176,985
Due in one to five years	27,117
Total	$ 204,102

Balance Sheet Details - Schedul

Balance Sheet Details - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 11,502	$ 7,369
Less: accumulated depreciation and amortization	(3,548)	(4,097)
Property and equipment, net	7,954	3,272
Furniture and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	1,619	397
Computers and Computer Software
Property Plant And Equipment [Line Items]
Total property and equipment	430	111
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	$ 9,453	4,739
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment		1,903
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment		$ 219

Balance Sheet Details - Additio

Balance Sheet Details - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 1,800,000	$ 1,400,000	$ 1,200,000
Capital lease amortization expense	$ 0	$ 0	$ 200,000

Balance Sheet Details - Sched_2

Balance Sheet Details - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Preclinical studies	$ 5,039	$ 2,844
Professional fees	400	490
Other accrued expenses	3,348	432
Total	$ 8,787	$ 3,766

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	1 Months Ended					12 Months Ended
	Feb. 28, 2022	Jan. 31, 2021RenewalOption	Nov. 30, 2020	Jul. 31, 2019	Jul. 31, 2016RenewalOption	Dec. 31, 2021USD ($)Lease	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Jan. 01, 2021USD ($)
Lessee Lease Description [Line Items]
Operating lease, ROU assets						$ 27,958			$ 900
Operating lease liabilities						$ 16,783			900
Number of operating lease | Lease						2
Operating leases, rent expense recognized						$ 3,200	$ 700	$ 600
ASU 2016-02
Lessee Lease Description [Line Items]
Operating lease, ROU assets									900
Operating lease liabilities									$ 900
Headquarters Facility
Lessee Lease Description [Line Items]
Operating lease, agreement term					5 years
Operating lease, commencement date					Sep. 1, 2016
Lease expiration date					Aug. 31, 2021
Operating lease, renewal option | RenewalOption					2
Operating lease, renewal term					30 months
Operating lease, option to renewal, description						30-month renewal options
Operating lease, existence of option to renewal					true
Operating lease, description						In July 2016, we entered into a five-year lease agreement for our previous headquarters facility located in Foster City, California. The original term of the lease was from September 1, 2016 to August 31, 2021, with two 30-month renewal options.
Operating lease, extended term			6 months
Operating lease, extended maturity date			Mar. 1, 2022
Headquarters Facility | Subsequent Event
Lessee Lease Description [Line Items]
Lease termination date	Feb. 12, 2022
Additional Facility
Lessee Lease Description [Line Items]
Operating lease, commencement date				Jul. 1, 2019
Lease expiration date				Oct. 31, 2021
Operating lease, option to renewal, description						no renewal options
Operating lease, existence of option to renewal				false
Operating lease, description						In July 2019, we leased another facility in Foster City, California as a result of growth in personnel and lab space requirements. The original term of this lease was from July 1, 2019 to October 31, 2021, with no renewal options.
Operating lease, extended term			6 months
Operating lease, extended maturity date			Apr. 30, 2022
Office
Lessee Lease Description [Line Items]
Lease expiration date						Apr. 30, 2021
New Corporate Headquarters Facility
Lessee Lease Description [Line Items]
Operating lease, commencement date		Jan. 22, 2021
Lease expiration date		Dec. 31, 2025
Operating lease, renewal term		60 months
Operating lease, extended term		60 days
Number of renewal options | RenewalOption		2
Palo Alto
Lessee Lease Description [Line Items]
Operating lease, extended maturity date		Mar. 3, 2022
Operating lease, ROU assets						$ 300
Operating lease liabilities						300
San Carlos
Lessee Lease Description [Line Items]
Operating lease, ROU assets						28,400
Operating lease liabilities						$ 12,900

Leases - Schedule of Informatio

Leases - Schedule of Information Related to ROU Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Jan. 01, 2021
Leases [Abstract]
Cash paid for operating lease liabilities	$ 924
Operating lease right-of-use assets	27,958	$ 900
Operating lease liabilities — current	5,276
Operating lease liabilities — long-term	11,507
Operating Lease, Liability, Total	$ 16,783	$ 900
Weighted-average remaining lease term (in years)	3 years 9 months
Weighted-average discount rate	7.50%

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Leases [Abstract]
2021			$ 742
2022	$ (105)
2023 and 2022	6,639		190
2024	6,805
2025	6,976
Total future undiscounted lease payments	20,315		$ 932
Less: Imputed interest	(3,532)
Lease liabilities	$ 16,783	$ 900

Leases - Schedule of Maturiti_2

Leases - Schedule of Maturities of Lease Liabilities (Parenthetical) (Details) $ in Millions	Dec. 31, 2021USD ($)
Palo Alto
Lessee Lease Description [Line Items]
Lease incentives	$ 0.9

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - Lonza DMSA - USD ($)	1 Months Ended
	Jun. 30, 2021	Apr. 30, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Percentage of defer payments agreed for completion		50.00%
Payments in equity, amount	$ 10,000,000
Amount recorded with respect to the potential future payments above the initial cash cap		$ 10,000,000	$ 0
Number of common stock issued	399,680
Public offering price per share	$ 25.02

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock - Additional Information (Details) - Redeemable Convertible Preferred Stock - shares	1 Months Ended
	Jun. 30, 2020	Dec. 31, 2021	Jun. 17, 2020
Temporary Equity [Line Items]
Preferred stock outstanding		0	0
Preferred stock authorized		0
Preferred stock converted into common stock	28,610,337

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jul. 31, 2021
Class Of Stock [Line Items]
Common stock, shares authorized	500,000,000	500,000,000
Common stock, par value per share	$ 0.001	$ 0.001
Common stock, shares issued	53,031,978	51,071,593
Common stock, shares outstanding	53,031,978	51,071,593
Common stock, dividends, per share, declared	$ 0	$ 0
Common stock, voting rights	Each share of common stock is entitled to one vote.
Proceeds from issuance of stock, net of commission and offering expenses	$ 13,896,000
Equity incentive plan, shares issued	62,382
ATM Sales Agreement | Jefferies LLC
Class Of Stock [Line Items]
Maximum commission percentage of gross proceeds from common stock sold			3.00%
Common stock shares sold	567,045
Average price	$ 25.26
Aggregate gross proceeds from issuance of common stock	$ 14,300,000
Proceeds from issuance of stock, net of commission and offering expenses	$ 13,900,000
ATM Sales Agreement | Maximum | Jefferies LLC
Class Of Stock [Line Items]
Aggregate offering price			$ 150,000,000

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Stock Shares Reserved for Future Issuance (Details) - 2020 Plan and 2014 Plan - shares	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock reserved for future issuances	11,399,763	9,839,680
Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuances	5,295,007	5,188,531
Shares Available for Future Stock Option Grants
Class Of Stock [Line Items]
Common stock reserved for future issuances	6,104,756	4,651,149

Warrants - Additional Informati

Warrants - Additional Information (Details)	Jun. 30, 2020shares
Equity [Abstract]
Warrant exercised	46,869

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 01, 2022	Jun. 11, 2020	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage for stock options granted		25.00%
Vesting period for stock options granted		4 years
Early exercised stock options				7,410	15,056
Options granted					62,382
Exercise of stock options (in shares)				926,514	358,264
Weighted-average price per share				$ 3.25	$ 1.88
Weighted-average grant date fair value of options granted				$ 14.65	$ 9.62
Intrinsic value of the stock options exercised				$ 18.9	$ 7.8
Unrecognized stock-based compensation expense				$ 27.5
Unrecognized share-based compensation expense, expected to be recognized				2 years 6 months
Performance-based Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense			$ 0.3
Performance-based Awards | IPO
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares vested			362,935
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price expire in years form the date of grant		5 years
Stock options granted term		10 years
Percentage of provisions subject to stockholders		10.00%
Shares reserved for issuance		10,150,000
Term of plan		10 years
Percentage of outstanding number of shares		5.00%
Aggregate number of shares available for issuance				6,104,756
Number of shares outstanding				1,637,613
2020 Equity Incentive Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Available for issuance of shares increased	2,651,598
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding				3,657,394
2020 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance		650,000
Term of plan		10 years
Percentage of outstanding number of shares		1.00%
Aggregate number of shares available for issuance				1,070,704
Employees purchase shares of common stock of lower of fair market value		85.00%
Offering period		2 years
Purchase period		6 months
Percentage of payroll deductions of eligible compensation		15.00%
Employees acquired shares of common stock				62,546
2020 Employee Stock Purchase Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Available for issuance of shares increased	530,319
Minimum | 2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Incentive stock option granted to employees owning percentage of shares of common stock		10.00%
Maximum | Other Liabilities
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining liabilities related to early exercised shares				$ 0.1	$ 0.1
Maximum | 2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of fair value per share on the grant date		110.00%

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of Activity Under Stock Option Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, granted		62,382
Weighted-Average Exercise Price Per Share, Options exercised	$ 3.25	$ 1.88
2020 Plan and 2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Available for Grant, Beginning Balance	4,651,149	835,941
Options Available for Grant, Additional shares authorized	2,553,579	5,997,435
Options Available for Grant, granted	(1,616,021)	(2,255,690)
Options Available for Grant, forfeited	516,049	73,463
Options Available for Grant, Ending Balance	6,104,756	4,651,149
Number of Options, Beginning Balance	5,121,549	3,297,586
Number of Options, granted	1,616,021	2,255,690
Number of Options, exercised	(926,514)	(358,264)
Number of Options, forfeited	(516,049)	(73,463)
Number of Options, Ending Balance	5,295,007	5,121,549
Number of Options, Vested and expected to vest	5,295,007
Number of Options, Exercisable	2,611,523
Weighted-Average Exercise Price Per Share, Beginning Balance	$ 4.99	$ 1.93
Weighted-Average Exercise Price Per Share, Options granted	21.83	8.93
Weighted-Average Exercise Price Per Share, Options exercised	3.25	1.88
Weighted-Average Exercise Price Per Share, Options forfeited	16.70	3.50
Weighted-Average Exercise Price Per Share, Ending Balance	9.30	$ 4.99
Weighted-Average Exercise Price Per Share, Vested and expected to vest	9.30
Weighted-Average Exercise Price Per Share, Exercisable	$ 4.76
Weighted-Average Remaining Contractual Term (Years)	7 years 10 months 20 days
Weighted-Average Remaining Contractual Term (Years), Vested and expected to vest	7 years 10 months 20 days
Weighted-Average Remaining Contractual Term (Years), Exercisable	7 years 25 days
Aggregate Intrinsic Value	$ 78,604
Aggregate Intrinsic Value, Vested and expected to vest	78,604
Aggregate Intrinsic Value, Exercisable	$ 50,123

Equity Incentive Plans - Summ_2

Equity Incentive Plans - Summary of Estimated Fair Value of Employee Stock Options (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assumptions
Expected volatility, Minimum	81.00%	81.20%	78.40%
Expected volatility, Maximum	84.10%	94.10%	80.40%
Expected dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate, Minimum	0.50%	0.30%	1.60%
Risk-free interest rate, Maximum	1.30%	1.40%	2.40%
Minimum
Fair Value Assumptions
Expected term (in years)	5 years 3 months 18 days	5 years 7 months 6 days	5 years 10 months 24 days
Maximum
Fair Value Assumptions
Expected term (in years)	5 years 6 months	6 years 1 month 6 days	6 years 1 month 6 days

Equity Incentive Plans - Summ_3

Equity Incentive Plans - Summary of Estimated Fair Value of Shares Under Employee Stock Purchase Plan (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assumptions
Expected volatility, Minimum	81.00%	81.20%	78.40%
Expected volatility, Maximum	84.10%	94.10%	80.40%
Expected dividend yield	0.00%	0.00%	0.00%
Risk-free interest rate, Minimum	0.50%	0.30%	1.60%
Risk-free interest rate, Maximum	1.30%	1.40%	2.40%
Minimum
Fair Value Assumptions
Expected term (in years)	5 years 3 months 18 days	5 years 7 months 6 days	5 years 10 months 24 days
Maximum
Fair Value Assumptions
Expected term (in years)	5 years 6 months	6 years 1 month 6 days	6 years 1 month 6 days
2020 Employee Stock Purchase Plan
Fair Value Assumptions
Expected volatility, Minimum	79.60%	105.80%
Expected volatility, Maximum	126.30%	158.20%
Expected dividend yield	0.00%	0.00%
Risk-free interest rate, Minimum	0.00%	0.10%
Risk-free interest rate, Maximum	0.50%	0.20%
2020 Employee Stock Purchase Plan | Minimum
Fair Value Assumptions
Expected term (in years)	6 months	4 months 24 days
2020 Employee Stock Purchase Plan | Maximum
Fair Value Assumptions
Expected term (in years)	2 years	2 years

Equity Incentive Plans - Summ_4

Equity Incentive Plans - Summary of Stock-based Compensation Expense (Details) - 2014 Plan, 2020 Plan and 2020 ESPP - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 10,729	$ 5,434	$ 1,185
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	3,954	1,861	368
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 6,775	$ 3,573	$ 817

Funding Arrangement - Additiona

Funding Arrangement - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Apr. 30, 2021	Jul. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 31, 2022	Aug. 04, 2021	Jul. 31, 2020
Funding Arrangement [Line Items]
Grant income			$ 1,585,000	$ 2,478,000	$ 237,000
Cost Reimbursement Sub-Award Agreement
Funding Arrangement [Line Items]
Funding period of award to develop universal vaccine to prevent infections caused by Group A Strep bacteria		4 years
Potential funding amount of award to develop vaccine to prevent shingella infections	$ 500,000
Grant income			1,600,000	2,500,000	$ 200,000
Cost Reimbursement Sub-Award Agreement | Maximum
Funding Arrangement [Line Items]
Initial funding committed by award		$ 1,600,000
Total funding committed by award, available upon achievement of development milestones		$ 15,100,000
Potential funding period of award to develop vaccine to prevent shingella infections	5 years
CARB-X Agreement
Funding Arrangement [Line Items]
Additional funding committed by award							$ 3,200,000
Grant receivable on unreimbursed, eligible costs incurred			$ 1,200,000	$ 300,000
CARB-X Agreement | Subsequent Event
Funding Arrangement [Line Items]
Potential funding committed by award						$ 13,900,000
CARB-X Agreement | Maximum
Funding Arrangement [Line Items]
Initial funding committed by award								$ 2,700,000
Additional funding committed by award							3,200,000
Potential funding committed by award							$ 29,700,000
CARB-X Agreement | Minimum
Funding Arrangement [Line Items]
Initial funding committed by award								$ 1,600,000

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net loss (in thousands)	$ (100,077)	$ (89,217)	$ (50,274)
Weighted-average shares outstanding used in computing net loss per share, basic and diluted	51,922,108	29,545,810	3,795,090
Net loss per share, basic and diluted	$ (1.93)	$ (3.02)	$ (13.25)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	5,357,389	5,188,531	23,845,796
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	5,357,389	5,188,531	3,364,568
Common Stock Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share			31,857
Redeemable Convertible Preferred Stock Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share			59,276
Series A Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share			6,225,719
Series B Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share			6,786,896
Series C Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share			7,377,480

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	[1]	Dec. 31, 2019	[1]
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Statutory Rate	21.00%	21.00%		21.00%
Stock-based Compensation	2.20%	0.80%		(0.40%)
Credits	1.10%	0.60%		(0.50%)
Change in Fair Value of Tranche Liability	0.00%	0.00%		1.30%
Change in valuation allowance	(23.00%)	(22.10%)		(21.80%)
Section 162(m) Limitation	(1.10%)	(0.10%)		0.00%
Other	(0.20%)	(0.20%)		0.40%
Total	0.00%	0.00%		0.00%
[1]	The 2019 and 2020 effective tax rate reconciliations have been updated to conform to the 2021 presentation.

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating losses	$ 85,574	$ 52,330
Fixed assets	1,700	528
Accruals & reserves	4,131	2,786
Credits	2,865	1,222
Section 59(e) Capitalized expenses	2,984	3,381
Accrued manufacturing expenses	1,006	3,374
Lease Liability	6,674
Total	104,934	63,621
Deferred tax liabilities:
ROU asset	(8,349)
Total deferred tax liabilities	(8,349)
Net deferred tax asset	96,585	63,621
Valuation allowance	$ (96,585)	$ (63,621)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Uncertain tax benefits	$ 924,000	$ 393,000	$ 271,000	$ 408,000
Interest or penalties recognized for the period	0	$ 0
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	296,700,000
Research credit carryforwards	$ 2,200,000
Tax credit carry forwards expiration year	2039
Federal | Research | Maximum
Income Tax Disclosure [Line Items]
Research credit carryforward	$ 100
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 262,700,000
Operating loss carry forwards expiration year	2034
California
Income Tax Disclosure [Line Items]
Research credit carryforwards	$ 1,600,000

Income Taxes - Reconciliation_2

Income Taxes - Reconciliation of Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Balance at the beginning of the year	$ 393	$ 271	$ 408
Additions based on tax positions related to current year	461	287	217
Adjustments based on tax positions related to prior years	70	(165)	(354)
Balance at end of year	$ 924	$ 393	$ 271

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	May 29, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2020
Related Party Transaction [Line Items]
Common stock, shares owned		53,031,978	51,071,593
Warrant exercised					46,869
Change in fair value of redeemable convertible preferred stock warrant			$ 179,000	$ (12,000)
Sutro Biopharma, Inc
Related Party Transaction [Line Items]
Common stock, shares owned		1,600,000	1,600,000
Accrued expenses payable		$ 0	$ 700,000
Sutro Biopharma, Inc | License Agreement
Related Party Transaction [Line Items]
Percentage of royalty payment on annual net sales of vaccine products for human health		4.00%
Percentage of royalty payment on net sales of vaccine compositions for animal health		2.00%
Sutro Biopharma, Inc | Supply Agreement
Related Party Transaction [Line Items]
Expenses related to agreement		$ 2,400,000	1,200,000	$ 1,100,000
Sutro Biopharma, Inc | Series C Redeemable Convertible Stock
Related Party Transaction [Line Items]
Warrant to purchase shares of stock				59,276
Warrant purchase price per share				$ 11.5215
Sutro Biopharma, Inc | Series C Redeemable Convertible Stock | License Amendment A2
Related Party Transaction [Line Items]
Warrant to purchase shares of stock	59,276
Warrant purchase price per share	$ 11.5215
Warrant exercisable and vests immediately and expires date	May 29, 2018
Sutro Biopharma, Inc | Common Stock
Related Party Transaction [Line Items]
Warrant to purchase shares of stock				31,857
Warrant purchase price per share				$ 0.79289
Sutro Biopharma, Inc | Common Stock Warrant
Related Party Transaction [Line Items]
Warrant exercised				30,278
Sutro Biopharma, Inc | Preferred Stock Warrant
Related Party Transaction [Line Items]
Warrant exercised				16,591
Change in fair value of redeemable convertible preferred stock warrant		$ 0	$ 200,000	$ 0

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event - Underwritten Public Offering - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Feb. 28, 2022	Jan. 31, 2022
Subsequent Event [Line Items]
Shares issued		2,500,000
Common stock price per share		$ 20
Pre-funded warrants to purchase shares		2,500,000
Pre-funded warrants price per share		$ 19.999
Net proceeds from follow on offering	$ 14.1	$ 93.5
Underwriters' option to purchase additional shares	750,000