Vaxcyte (PCVX) 10-Q 10 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 08, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Registrant Name	VAXCYTE, INC.
Entity Central Index Key	0001649094
Current Fiscal Year End Date	--12-31
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity File Number	001-39323
Entity Tax Identification Number	46-4233385
Entity Address, Address Line One	353 Hatch Drive
Entity Address, City or Town	Foster City
Entity Address, State or Province	CA
Entity Incorporation, State or Country Code	DE
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	837-0111
Document Quarterly Report	true
Document Transition Report	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		52,785,136
Entity Filer Category	Non-accelerated Filer
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	PCVX
Security Exchange Name	NASDAQ

Condensed Balance Sheets (Unaud

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 112,044	$ 386,200
Short-term investments	166,532
Prepaid expenses and other current assets	24,373	2,804
Total current assets	302,949	389,004
Property and equipment, net	6,626	3,272
Operating lease right-of-use assets	307
Long-term investments	39,735
Restricted cash	871
Other assets	3,580	550
Total noncurrent assets	51,119	3,822
Total assets	354,068	392,826
Current liabilities:
Accounts payable	25,713	29,785
Accrued compensation	2,075	284
Accrued manufacturing expenses	7,033	13,012
Accrued expenses (including related party accrual of $0 and $677 as of September 30, 2021 and December 31, 2020, respectively)	12,027	3,766
Deferred rent — current		14
Operating lease liabilities — current	613
Total current liabilities	47,461	46,861
Deferred rent — long-term		10
Operating lease liabilities — long-term	553
Other liabilities	98	112
Total liabilities	48,112	46,983
Commitments and contingencies (Note 6)
Stockholders' Equity
Preferred stock, $0.001 par value — 10,000,000 shares authorized at September 30, 2021 and December 31, 2020; no shares issued and outstanding at September 30, 2021 and December 31, 2020
Common stock, $0.001 par value — 500,000,000 shares authorized at September 30, 2021 and December 31, 2020; 52,587,855 and 51,071,593 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively	56	54
Additional paid-in capital	575,990	544,353
Accumulated other comprehensive loss	(12)
Accumulated deficit	(270,078)	(198,564)
Total stockholders' equity	305,956	345,843
Total liabilities, redeemable convertible preferred stock and stockholders' equity	$ 354,068	$ 392,826

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Sep. 30, 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	52,587,855	51,071,593
Common stock, shares outstanding	52,587,855	51,071,593

Condensed Statements of Operati

Condensed Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development (including related party expenses of $0 and $143 for the three months ended September 30, 2021 and 2020, respectively, and $2,359 and $458 for the nine months ended September 30, 2021 and 2020, respectively)	$ 20,428	$ 16,410	$ 55,337	$ 58,903
General and administrative	6,523	4,898	18,487	11,225
Total operating expenses	26,951	21,308	73,824	70,128
Loss from operations	(26,951)	(21,308)	(73,824)	(70,128)
Other income (expense), net:
Interest expense			(7)	(7)
Interest income	90	33	245	212
Grant income	299	787	677	2,152
Realized gain on marketable securities	1		2
Foreign currency transaction gains (losses)	(54)	(530)	1,393	(709)
Total other income (expense), net	336	290	2,310	1,648
Net loss	$ (26,615)	$ (21,018)	$ (71,514)	$ (68,480)
Net loss per share, basic and diluted	$ (0.51)	$ (0.41)	$ (1.39)	$ (3.06)
Weighted-average shares outstanding, basic and diluted	52,187,303	50,895,358	51,627,249	22,354,212

Condensed Statements of Opera_2

Condensed Statements of Operations (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Research and development expense to related party	$ 0	$ 143	$ 2,359	$ 458

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net Loss	$ (26,615)	$ (21,018)	$ (71,514)	$ (68,480)
Other comprehensive loss:
Unrealized gains (losses) on investments	(4)		(12)
Comprehensive loss	$ (26,619)	$ (21,018)	$ (71,526)	$ (68,480)

Condensed Statements of Redeema

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	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, 2019	$ (106,373)	$ 7	$ 2,967	$ (109,347)
Beginning balance, shares at Dec. 31, 2019		4,059,909
Beginning balance at Dec. 31, 2019						$ 24,967	$ 55,151	$ 80,192
Beginning balance, shares at Dec. 31, 2019						6,225,719	6,786,896	7,377,480
Exercise of stock options	49		49
Exercise of stock options (in shares)		28,837
Issuance of common stock related to early exercised stock options		14,819
Vesting of early exercised stock options	128		128
Issuance of preferred stock									$ 109,875
Issuance of preferred stock, net of issuance cost (in shares)									8,220,242
Stock-based compensation expense	372		372
Net Loss	(27,142)			(27,142)
Ending balance at Mar. 31, 2020	(132,966)	$ 7	3,516	(136,489)
Ending balance, shares at Mar. 31, 2020		4,103,565
Ending balance at Mar. 31, 2020						$ 24,967	$ 55,151	$ 80,192	$ 109,875
Ending balance, shares at Mar. 31, 2020						6,225,719	6,786,896	7,377,480	8,220,242
Beginning balance at Dec. 31, 2019	(106,373)	$ 7	2,967	(109,347)
Beginning balance, shares at Dec. 31, 2019		4,059,909
Beginning balance at Dec. 31, 2019						$ 24,967	$ 55,151	$ 80,192
Beginning balance, shares at Dec. 31, 2019						6,225,719	6,786,896	7,377,480
Net Loss	(68,480)
Ending balance at Sep. 30, 2020	364,075	$ 54	541,848	(177,827)
Ending balance, shares at Sep. 30, 2020		50,949,490
Beginning balance at Mar. 31, 2020	(132,966)	$ 7	3,516	(136,489)
Beginning balance, shares at Mar. 31, 2020		4,103,565
Beginning balance at Mar. 31, 2020						$ 24,967	$ 55,151	$ 80,192	$ 109,875
Beginning balance, shares at Mar. 31, 2020						6,225,719	6,786,896	7,377,480	8,220,242
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	264,079	$ 18	264,061
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs (in shares)		17,968,750
Exercise of stock options	297		297
Exercise of stock options (in shares)		152,177
Vesting of early exercised stock options	12		12
Issuance costs		$ (3,296)
Issuance of preferred stock									$ 4
Stock-based compensation expense	1,289		1,289
Net Loss	(20,320)			(20,320)
Ending balance at Jun. 30, 2020	383,210	$ 54	539,965	(156,809)
Ending balance, shares at Jun. 30, 2020		50,881,698
Exercise of stock options	108		108
Exercise of stock options (in shares)		67,792
Vesting of early exercised stock options	9		9
Issuance costs	(72)		(72)
Stock-based compensation expense	1,838		1,838
Net Loss	(21,018)			(21,018)
Ending balance at Sep. 30, 2020	364,075	$ 54	541,848	(177,827)
Ending balance, shares at Sep. 30, 2020		50,949,490
Beginning balance at Dec. 31, 2020	345,843	$ 54	544,353	(198,564)
Beginning balance, shares at Dec. 31, 2020		51,071,593
Exercise of stock options	487		487
Exercise of stock options (in shares)		267,208
Vesting of early exercised stock options	9		9
Stock-based compensation expense	1,865		1,865
Unrealized gains (losses) on investments	(47)				$ (47)
Net Loss	(21,220)			(21,220)
Ending balance at Mar. 31, 2021	326,937	$ 54	546,714	(219,784)	(47)
Ending balance, shares at Mar. 31, 2021		51,338,801
Beginning balance at Dec. 31, 2020	345,843	$ 54	544,353	(198,564)
Beginning balance, shares at Dec. 31, 2020		51,071,593
Net Loss	(71,514)
Ending balance at Sep. 30, 2021	305,956	$ 56	575,990	(270,078)	(12)
Ending balance, shares at Sep. 30, 2021		52,587,855
Beginning balance at Mar. 31, 2021	326,937	$ 54	546,714	(219,784)	(47)
Beginning balance, shares at Mar. 31, 2021		51,338,801
Exercise of stock options	466		466
Exercise of stock options (in shares)		190,003
Vesting of early exercised stock options	2		2
Issuance of common stock under Employee Stock Purchase Plan	490		490
Issuance of common stock under Employee Stock Purchase Plan (in shares)		35,286
Issuance of common stock to Lonza Ltd.	10,001	$ 1	10,000
Issuance of common stock to Lonza Ltd. (in shares)		399,680
Stock-based compensation expense	2,769		2,769
Unrealized gains (losses) on investments	39				39
Net Loss	(23,679)			(23,679)
Ending balance at Jun. 30, 2021	317,025	$ 55	560,441	(243,463)	(8)
Ending balance, shares at Jun. 30, 2021		51,963,770
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs	12,120	$ 1	12,119
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs (in shares)		498,502
Exercise of stock options	491		491
Exercise of stock options (in shares)		125,583
Vesting of early exercised stock options	2		2
Issuance costs		$ (41)
Stock-based compensation expense	2,937		2,937
Unrealized gains (losses) on investments	(4)				(4)
Net Loss	(26,615)			(26,615)
Ending balance at Sep. 30, 2021	$ 305,956	$ 56	$ 575,990	$ (270,078)	$ (12)
Ending balance, shares at Sep. 30, 2021		52,587,855

Condensed Statements of Redee_2

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2020USD ($)
Series D Redeemable Convertible Preferred Stock
Issuance costs	$ 125

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (71,514)	$ (68,480)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,341	1,073
Stock-based compensation expense	7,571	3,499
Change in fair value of redeemable convertible preferred stock warrant		179
Amortization of operating right-of-use assets	910
Net amortization of premiums on investments	910
Loss on disposal of fixed assets	32	32
Asset impairment charges		267
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(16,306)	(1,040)
Other assets	(3,030)	33
Operating lease liabilities	(75)
Accounts payable	5,601	7,330
Accrued compensation	1,791	1,076
Accrued manufacturing expenses	(5,979)	18,763
Accrued expenses	8,448	1,416
Deferred rent and other long-term liabilities		(8)
Net cash used in operating activities	(70,300)	(35,860)
Cash flows from investing activities:
Purchases of property and equipment	(5,173)	(433)
Proceeds from sale of property and equipment		50
Purchases of investments	(295,279)
Maturities of investments	58,000
Sales of investments	30,062
Net cash used in investing activities	(212,390)	(383)
Cash flows from financing activities:
Payments of capital lease obligations		(61)
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
Proceeds from exercise of common stock options	1,444	454
Proceeds from issuance of common stock related to at-the-market offering, net of issuance costs	7,108
Proceeds from issuance of common stock related to early exercised stock options		36
Proceeds from issuance of common stock under the Employee Stock Purchase Plan	490
Net cash provided by financing activities	9,042	374,315
Effect of exchange rate changes on cash and cash equivalents	363
Net (decrease) increase in cash, cash equivalents and restricted cash	(273,285)	338,072
Cash, cash equivalents and restricted cash, beginning of period	386,200	58,976
Cash, cash equivalents and restricted cash, end of period	112,915	397,048
Supplemental disclosure of cash flow information:
Cash paid for interest	7	7
Supplemental disclosures of non-cash investing and financing activities:
Purchases of property and equipment recorded in accounts payable and accrued expenses	271	149
Conversion of convertible preferred stock into common stock		270,190
Issuance costs for initial public offering included in accounts payable and accrued expenses		$ 17
Stock issued for payment of accounts payable	10,000
Deferred offering costs included in accounts payable and accrued expenses	154
Proceeds from issuance of common stock through ATM facility not yet received	$ 5,011

Company Organization and Nature

Company Organization and Nature of Business	9 Months Ended
	Sep. 30, 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 Foster City, 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 next-generation vaccine company seeking to improve global health by developing superior and novel vaccines designed to prevent or treat some of the most common and deadly infectious diseases worldwide. Our cell-free protein synthesis platform enables us to design and produce protein carriers and antigens, the critical building blocks of vaccines, in ways that we believe conventional vaccine technologies currently cannot. Our pipeline includes pneumococcal conjugate vaccine (“PCV”) candidates that we believe are among the most broad-spectrum PCV candidates currently in development, targeting the $7 billion global pneumococcal vaccine market. Our lead vaccine candidate, VAX-24, is a 24-valent investigational PCV. We anticipate submitting our initial investigational new drug (“IND”) application to the U.S. Food and Drug Administration (“FDA”) for VAX-24 in the first quarter of 2022, following the anticipated completion of the remaining drug product testing and release, as well as documentation of stability, and initiating our Phase 1/2 clinical proof-of-concept study in adults thereafter. We expect to announce topline data from this study between late 2022 and early 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 at least 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 for 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 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 On June 11, 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	9 Months Ended
	Sep. 30, 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 condensed 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 interim financial reporting. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted in accordance with such rules and regulations. Unaudited Interim Condensed Financial Statements The condensed balance sheet as of September 30, 2021 and the condensed statements of operations, comprehensive loss, redeemable convertible preferred stock and stockholders’ equity for the three and nine months ended September 30, 2021 and 2020 and the condensed statements of cash flows for the nine months ended September 30, 2021 and 2020 are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of our financial information. The financial data disclosed in the footnotes to the condensed financial statements related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other future annual or interim period. These interim condensed financial statements should be read in conjunction with our audited financial statements and related notes thereto for the year ended December 31, 2020 included in our Annual Report on Form 10-K filed with the SEC on March 29, 2021. 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 determination of our 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. 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. Investments Our investments have been classified and accounted for as available-for-sale securities. Fixed income securities 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 condensed balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive income. 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. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented. 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 such equity transactions, these deferred offering costs were included in Other assets on the condensed balance sheet. In connection with and as of the closing of such equity transactions, these costs were reclassified to Additional paid-in capital, representing a reduction to the gross proceeds. As of September 30, 2021, $3.4 million of IPO-related costs are included in the Additional paid-in capital line item on the condensed balance sheet. As of September 30, 2021 and December 31, 2020, we recorded deferred offering costs of $0.5 million and $0.1 million, respectively, in Other assets on the condensed balance sheets. Leases Under Financial Accounting Standards Board (FASB) Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) 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 September 30 , 2021, our lease population consisted of real estate operating leases . As of September 30 , 2021, the Company did no t have finance leases. Operating leases are included in Operating lease right-of-use (ROU) assets, Operating lease liabilities — — 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 condensed 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 Quarterly Report on Form 10-Q. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASC 842, which 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 will be classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement. The new standard is effective for us on January 1, 2022, with early adoption permitted. 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, allows the carryforward of historical lease classifications. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740) 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

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 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 condensed 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 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 ou r 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 determination s 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 September 30, 2021 or December 31, 2020 . There were no 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 September 30, 2021 and December 31, 2020: September 30, 2021 Fair Value Hierarchy Level Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 52,611 $ — $ — $ 52,611 Money market funds (1) Level 1 51,183 — — 51,183 Commercial paper (1) Level 2 8,250 — — 8,250 Total cash and cash equivalents 112,044 — — 112,044 Investments: U.S. Treasury securities Level 1 43,390 11 — 43,401 Commercial paper Level 2 69,966 — (1 ) 69,965 Corporate debt Level 2 54,213 — (16 ) 54,197 Asset-backed securities Level 2 13,958 — (7 ) 13,951 U.S. government agency securities Level 2 24,752 1 — 24,753 Total investments 206,279 12 (24 ) 206,267 Total assets measured at fair value $ 318,323 $ 12 $ (24 ) $ 318,311 December 31, 2020 Fair Value Hierarchy Level Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 4,788 $ — $ — $ 4,788 Money market funds (1) Level 1 381,412 — — 381,412 Total assets measured at fair value $ 386,200 $ — $ — $ 386,200 (1) Included within cash and cash equivalents on the condensed balance sheets. The following table presents the contractual maturities of our investments as of September 30, 2021 (in thousands): September 30, 2021 Fair Value Due in less than one year $ 166,532 Due in one to five years 39,735 Total $ 206,267

Balance Sheet Details

Balance Sheet Details	9 Months Ended
	Sep. 30, 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 September 30, 2021 and December 31, 2020 consisted of the following: September 30, December 31, 2021 2020 (in thousands) Furniture and equipment $ 1,217 $ 397 Computers and computer software 111 111 Lab equipment 8,814 4,739 Leasehold improvements 1,903 1,903 Construction in progress — 219 Total property and equipment 12,045 7,369 Less: accumulated depreciation and amortization (5,419 ) (4,097 ) Property and equipment, net $ 6,626 $ 3,272 Depreciation and amortization expense for the three months ended September 30, 2021 and 2020 was $0.5 million and $0.3 million, respectively. Depreciation and amortization expense for the nine months ended September 30, 2021 and 2020 was $1.3 million and $1.1 million, respectively. Accrued Expenses Accrued expenses as of September 30, 2021 and December 31, 2020 consisted of the following: September 30, December 31, 2021 2020 (in thousands) Preclinical studies $ 6,335 $ 2,844 Professional fees 643 490 Other accrued expenses 5,049 432 Total $ 12,027 $ 3,766

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	5. Leases Operating Lease Obligations In July 2016, we entered into a five-year In January 2021, we entered into a lease agreement for our new corporate headquarters facility to be 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 will expire 48 months from the first day of the first full month following the earlier to occur of (i) January 21, 2022 or (ii) the date that the tenant improvements are substantially completed. We have two 60-month renewal options. The license agreement for temporary space in Palo Alto will terminate when the San Carlos office leasehold improvements are completed and we move into our new corporate headquarters. These two leases 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 a ssets and lease liabilities are recognized based on the present value of the fixed and in-substance fixed lease payments over the lease term s at the ir respective commencement date s . 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 right-of-use asset and lease liability of $0.3 million and $0.3 million, respectively. The right-of-use asset and lease liability associated with the San Carlos lease will be recorded upon the date that the tenant improvements are substantially completed, which we anticipate will occur by the end of 2021 or early 2022. Because the Palo Alto and the San Carlos leases 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): September 30, 2021 Cash paid for operating lease liabilities $ 920 Operating lease right-of-use assets 307 Current operating lease liabilities $ 613 Non-current operating lease liabilities 553 Total lease liabilities $ 1,166 Weighted-average remaining lease term (in years) 0.32 Weighted-average discount rate 7.2 % Maturities of lease liabilities as of September 30, 2021 were as follows: Years ending December 31, (in thousands) Remainder of 2021 (1) $ (253 ) 2022 487 2023 379 2024 388 2025 398 Thereafter Total future undiscounted lease payments 1,399 Less: Imputed interest (233 ) Total lease liabilities $ 1,166 (1) Maturities for 2021 is 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 $1.0 million and $0.2 million for the three months ended September 30, 2021 and 2020, respectively, and $1.9 million and $0.5 million for the nine months ended September 30, 2021 and 2020, respectively.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 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 September 30, 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 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. In June 2018, we and Lonza entered into a letter agreement pursuant to which we agreed to certain terms for potential future 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 would 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, provided that (i) Lonza had the right to receive up to 25% of pre-IND payments in shares of our common stock, up to a maximum of $2.5 million, and (ii) we had the right to issue no more than $10.0 million of pre-IND payments in shares of our common stock. The Initial Cash Cap had not been reached as of December 31, 2020 As such, no amount had been 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 will pay Lonza agreed-upon fees for Lonza’s performance of manufacturing services, and we will 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	9 Months Ended
	Sep. 30, 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 September 30, 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	9 Months Ended
	Sep. 30, 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 52,587,855 and 51,071,593 shares were issued and outstanding as of September 30, 2021 and December 31, 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 September 30, 2021 and December 31, 2020, no dividends had been declared. Each share of common stock is entitled to one vote. In July 2021, we entered into an Open Market Sales Agreement SM Common stock reserved for future issuance 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: September 30, December 31, 2021 2020 Options issued and outstanding 5,427,007 5,188,531 Shares available for future stock option grants 6,321,076 4,651,149 Total 11,748,083 9,839,680

Warrants

Warrants	9 Months Ended
	Sep. 30, 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	9 Months Ended
	Sep. 30, 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 on terms consistent with stock options granted to new employees or 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 will be automatically increased on the first day of each calendar year during the ten-year 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 . As of September 30, 2021 , 3,961,387 shares and 1,465,620 shares of common stock were subject to outstanding options under the 2014 Plan and 2020 Plan, respectively . 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 condensed balance sheet and is reclassified to common stock and additional paid-in capital as such shares vest. At September 30, 2021 and December 31, 2020, 8,337 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 September 30, 2021 and December 31, 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 Available for Grant Number of Options Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Balances — December 31, 2020 4,651,149 5,121,549 $ 4.99 Additional shares authorized 2,553,579 — Options granted (1,378,321 ) 1,378,321 $ 21.46 Options exercised — (578,194 ) $ 2.50 Options forfeited 494,669 (494,669 ) $ 16.53 Balances — September 30, 2021 6,321,076 5,427,007 $ 8.39 7.71 $ 93,459 Vested and expected to vest — September 30, 2021 5,427,007 $ 8.39 7.71 $ 93,459 Exercisable at September 30, 2021 2,646,355 $ 4.03 6.59 $ 56,584 During the three months ended September 30, 2021 and 2020, 125,583 and 67,792 shares of stock options, respectively, were exercised for cash at a weighted-average price per share of $3.91 and $1.60, respectively. The weighted-average grant date fair value of options granted for the three months ended September 30, 2021 and 2020 was $17.00 and $29.83, respectively. The intrinsic value of the stock options exercised was $2.5 million and $2.5 million for the three months ended September 30, 2021 and 2020, During the nine months ended September 30, 2021 and 2020, 578,194 and 263,626 shares of stock options, respectively, were exercised for cash at a weighted-average price per share of $2.50 and $1.86, respectively. The weighted-average grant date fair value of options granted for the nine months ended September 30, 2021 and 2020 was $14.37 and $8.17, respectively. The intrinsic value of the stock options exercised was $12.4 million and $5.1 million for the nine months ended September 30, 2021 and 2020, 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 enrolled in the 2020 ESPP 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 two-year ten-year st Stock-based Compensation We estimated the fair value of employee stock options using the Black-Scholes option-pricing model for the three and nine months ended September 30, 2021 and 2020using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair Value Assumptions Expected volatility 81.2% - 81.8% 93.0% - 93.5% 81.0% - 82.5% 81.2% - 93.5% Expected dividend yield 0% 0% 0% 0% Expected term (in years) 5.4 5.6 5.4 - 5.5 5.6 - 6.1 Risk-free interest rate 0.8% - 1.1% 0.3% 0.5% - 1.1% 0.3% - 1.4% We estimated the fair value of shares under the 2020 ESPP using the Black-Scholes option-pricing model for the three and nine months ended September 30, 2021 and 2020 using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair Value Assumptions Expected volatility 79.6% - 88.8% 109.7% - 158.2% 79.6% - 126.3% 107.0% - 158.2% Expected dividend yield 0% 0% 0% 0% Expected term (in years) 0.5 - 2.0 0.4 - 1.9 0.5 - 2.0 0.4 - 1.9 Risk-free interest rate 0% - 0.2% 0.2% 0% - 0.2% 0.2% We recorded total stock-based compensation expense for the three and nine months ended September 30, 2021 and 2020 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the condensed statements of operations and allocated the amounts as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) (In thousands) Research and development $ 1,023 $ 558 $ 2,688 $ 1,081 General and administrative 1,914 1,280 4,883 2,418 Total $ 2,937 $ 1,838 $ 7,571 $ 3,499 Upon our IPO, 362,935 shares of 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 nine months ended September 30, 2020.

Funding Arrangement

Funding Arrangement	9 Months Ended
	Sep. 30, 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 commits 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 April 2021, we received a cost-reimbursement research award from 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 $0.3 million and $0.8 million of grant income under the CARB-X and Shigella awards and recorded the amounts in Other income (expense), net in the condensed statement of operations during the three months ended September 30, 2021 and 2020, respectively, and $0.7 million and $2.2 million during the nine months ended September 30, 2021 and 2020, respectively. A grant receivable of $0.7 million and $0.3 million representing unreimbursed, eligible costs incurred under the CARB-X and Shigella agreements was recorded and included in Prepaid expenses and other current assets in the condensed balance sheets as of September 30, 2021 and December 31, 2020, respectively.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 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: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net loss (in thousands) $ (26,615 ) $ (21,018 ) $ (71,514 ) $ (68,480 ) Weighted-average shares outstanding used in computing net loss per share, basic and diluted 52,187,303 50,895,358 51,627,249 22,354,212 Net loss per share, basic and diluted $ (0.51 ) $ (0.41 ) $ (1.39 ) $ (3.06 ) Potentially dilutive securities outstanding as of the periods presented below were excluded from the computation of diluted net loss per share for the three and nine months ended September 30, 2021 and 2020 because including them would have been antidilutive: As of September 30, 2021 2020 Stock options 5,489,389 5,094,669

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes In determining quarterly provisions for income taxes, we use the annual estimated effective tax rate applied to the actual year-to-date profit or loss, adjusted for discrete items arising in that period. Our annual estimated effective tax rate differs from the U.S. federal statutory rate primarily as a result of state taxes and changes in our valuation allowance against our deferred tax assets. For all periods presented, we have incurred net pre-tax losses in the United States. During the three and nine months ended September 30, 2021, there were no material changes to our unrecognized tax benefits, and we do not expect to have any significant changes to unrecognized tax benefits through the end of the fiscal year. For the three and nine months ended September 30, 2021, we reported zero tax provision. 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 (the “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 (“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 our current tax provision.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 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 September 30, 2021 and December 31, 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, which was amended in February 2021 (the “Sutro Biopharma Supply Agreement”). As of June 2, 2021, Sutro Biopharma was no longer considered as 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 E. coli 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. As Sutro Biopharma was no longer considered a related party as of June 2, 2021, we excluded expenses after that date from related party transaction expenses. We recognized expenses related to the Supply Agreement of $0 and $0.1 million for the three months ended September 30, 2021 and 2020, respectively, and $2.4 million and $0.3 million for the nine months ended September 30, 2021 and 2020, respectively. No amounts were recorded for changes in the fair value of the Preferred Stock Warrant for the three months ended September 30, 2021 and 2020. We recorded $0 and $0.2 million in changes in the fair value of the Preferred Stock Warrant for the nine months ended September 30, 2021 and 2020, respectively.

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These condensed 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 interim financial reporting. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted in accordance with such rules and regulations.
Unaudited Interim Condensed Financial Statements	Unaudited Interim Condensed Financial Statements The condensed balance sheet as of September 30, 2021 and the condensed statements of operations, comprehensive loss, redeemable convertible preferred stock and stockholders’ equity for the three and nine months ended September 30, 2021 and 2020 and the condensed statements of cash flows for the nine months ended September 30, 2021 and 2020 are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of our financial information. The financial data disclosed in the footnotes to the condensed financial statements related to the three and nine months ended September 30, 2021 and 2020 are also unaudited. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other future annual or interim period. These interim condensed financial statements should be read in conjunction with our audited financial statements and related notes thereto for the year ended December 31, 2020 included in our Annual Report on Form 10-K filed with the SEC on March 29, 2021.
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 determination of our 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.
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.
Investments	Investments Our investments have been classified and accounted for as available-for-sale securities. Fixed income securities 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 condensed balance sheets at fair value. Unrealized gains and losses on these securities are included as a separate component of accumulated other comprehensive income. 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.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.
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 such equity transactions, these deferred offering costs were included in Other assets on the condensed balance sheet. In connection with and as of the closing of such equity transactions, these costs were reclassified to Additional paid-in capital, representing a reduction to the gross proceeds. As of September 30, 2021, $3.4 million of IPO-related costs are included in the Additional paid-in capital line item on the condensed balance sheet. As of September 30, 2021 and December 31, 2020, we recorded deferred offering costs of $0.5 million and $0.1 million, respectively, in Other assets on the condensed balance sheets.
Leases	Leases Under Financial Accounting Standards Board (FASB) Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) 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 September 30 , 2021, our lease population consisted of real estate operating leases . As of September 30 , 2021, the Company did no t have finance leases. Operating leases are included in Operating lease right-of-use (ROU) assets, Operating lease liabilities — —
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 condensed 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 Quarterly Report on Form 10-Q.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASC 842, which 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 will be classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement. The new standard is effective for us on January 1, 2022, with early adoption permitted. 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, allows the carryforward of historical lease classifications. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740) 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

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2021 and December 31, 2020: September 30, 2021 Fair Value Hierarchy Level Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 52,611 $ — $ — $ 52,611 Money market funds (1) Level 1 51,183 — — 51,183 Commercial paper (1) Level 2 8,250 — — 8,250 Total cash and cash equivalents 112,044 — — 112,044 Investments: U.S. Treasury securities Level 1 43,390 11 — 43,401 Commercial paper Level 2 69,966 — (1 ) 69,965 Corporate debt Level 2 54,213 — (16 ) 54,197 Asset-backed securities Level 2 13,958 — (7 ) 13,951 U.S. government agency securities Level 2 24,752 1 — 24,753 Total investments 206,279 12 (24 ) 206,267 Total assets measured at fair value $ 318,323 $ 12 $ (24 ) $ 318,311 December 31, 2020 Fair Value Hierarchy Level Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 4,788 $ — $ — $ 4,788 Money market funds (1) Level 1 381,412 — — 381,412 Total assets measured at fair value $ 386,200 $ — $ — $ 386,200 (1) Included within cash and cash equivalents on the condensed balance sheets.
Schedule of Contractual Maturities of Investments	The following table presents the contractual maturities of our investments as of September 30, 2021 (in thousands): September 30, 2021 Fair Value Due in less than one year $ 166,532 Due in one to five years 39,735 Total $ 206,267

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net as of September 30, 2021 and December 31, 2020 consisted of the following: September 30, December 31, 2021 2020 (in thousands) Furniture and equipment $ 1,217 $ 397 Computers and computer software 111 111 Lab equipment 8,814 4,739 Leasehold improvements 1,903 1,903 Construction in progress — 219 Total property and equipment 12,045 7,369 Less: accumulated depreciation and amortization (5,419 ) (4,097 ) Property and equipment, net $ 6,626 $ 3,272
Schedule of Accrued Expenses	Accrued expenses as of September 30, 2021 and December 31, 2020 consisted of the following: September 30, December 31, 2021 2020 (in thousands) Preclinical studies $ 6,335 $ 2,844 Professional fees 643 490 Other accrued expenses 5,049 432 Total $ 12,027 $ 3,766

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 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): September 30, 2021 Cash paid for operating lease liabilities $ 920 Operating lease right-of-use assets 307 Current operating lease liabilities $ 613 Non-current operating lease liabilities 553 Total lease liabilities $ 1,166 Weighted-average remaining lease term (in years) 0.32 Weighted-average discount rate 7.2 %
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities as of September 30, 2021 were as follows: Years ending December 31, (in thousands) Remainder of 2021 (1) $ (253 ) 2022 487 2023 379 2024 388 2025 398 Thereafter Total future undiscounted lease payments 1,399 Less: Imputed interest (233 ) Total lease liabilities $ 1,166 (1) Maturities for 2021 is 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)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Schedule of Common Stock Shares Reserved for Future Issuance	Common stock reserved for future issuance 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: September 30, December 31, 2021 2020 Options issued and outstanding 5,427,007 5,188,531 Shares available for future stock option grants 6,321,076 4,651,149 Total 11,748,083 9,839,680

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 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 three and nine months ended September 30, 2021 and 2020using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair Value Assumptions Expected volatility 81.2% - 81.8% 93.0% - 93.5% 81.0% - 82.5% 81.2% - 93.5% Expected dividend yield 0% 0% 0% 0% Expected term (in years) 5.4 5.6 5.4 - 5.5 5.6 - 6.1 Risk-free interest rate 0.8% - 1.1% 0.3% 0.5% - 1.1% 0.3% - 1.4%
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 Available for Grant Number of Options Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value Balances — December 31, 2020 4,651,149 5,121,549 $ 4.99 Additional shares authorized 2,553,579 — Options granted (1,378,321 ) 1,378,321 $ 21.46 Options exercised — (578,194 ) $ 2.50 Options forfeited 494,669 (494,669 ) $ 16.53 Balances — September 30, 2021 6,321,076 5,427,007 $ 8.39 7.71 $ 93,459 Vested and expected to vest — September 30, 2021 5,427,007 $ 8.39 7.71 $ 93,459 Exercisable at September 30, 2021 2,646,355 $ 4.03 6.59 $ 56,584
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 three and nine months ended September 30, 2021 and 2020 using the following weighted-average assumptions: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Fair Value Assumptions Expected volatility 79.6% - 88.8% 109.7% - 158.2% 79.6% - 126.3% 107.0% - 158.2% Expected dividend yield 0% 0% 0% 0% Expected term (in years) 0.5 - 2.0 0.4 - 1.9 0.5 - 2.0 0.4 - 1.9 Risk-free interest rate 0% - 0.2% 0.2% 0% - 0.2% 0.2%
2014 Plan, 2020 Plan and 2020 ESPP
Summary of Stock-based Compensation Expense	We recorded total stock-based compensation expense for the three and nine months ended September 30, 2021 and 2020 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the condensed statements of operations and allocated the amounts as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (In thousands) (In thousands) Research and development $ 1,023 $ 558 $ 2,688 $ 1,081 General and administrative 1,914 1,280 4,883 2,418 Total $ 2,937 $ 1,838 $ 7,571 $ 3,499

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 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: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Net loss (in thousands) $ (26,615 ) $ (21,018 ) $ (71,514 ) $ (68,480 ) Weighted-average shares outstanding used in computing net loss per share, basic and diluted 52,187,303 50,895,358 51,627,249 22,354,212 Net loss per share, basic and diluted $ (0.51 ) $ (0.41 ) $ (1.39 ) $ (3.06 )
Schedule of Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share	Potentially dilutive securities outstanding as of the periods presented below were excluded from the computation of diluted net loss per share for the three and nine months ended September 30, 2021 and 2020 because including them would have been antidilutive: As of September 30, 2021 2020 Stock options 5,489,389 5,094,669

Company Organization and Natu_2

Company Organization and Nature of Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Jun. 15, 2020shares	Jun. 11, 2020USD ($)$ / sharesshares	Jun. 05, 2020	Jun. 30, 2020shares	Sep. 30, 2021shares	Jun. 30, 2020shares	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	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		0
Common Stock
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Shares issued and sold					498,502	17,968,750
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]
Shares issued and sold		17,968,750
Underwriters’ option to purchase additional shares		2,343,750
Public offering price per share | $ / shares		$ 16
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_3

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)Lease	Jan. 01, 2021USD ($)	Dec. 31, 2020USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Number of finance lease | Lease	0
ROU assets	$ 307	$ 900
Lease liabilities	$ 1,166	900
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 material impact	true
Accounting standard update adoption date	Jan. 1, 2021
ROU assets		900
Lease liabilities		$ 900
ASU 2019-12
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounting standard update material impact	true
Accounting standard update adoption date	Jan. 1, 2021
Accounting standard update adopted	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

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)Security	Sep. 30, 2021USD ($)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	$ 0
Fair value assets transferred from level 2 to level 1	0	0	0
Fair value liabilities transferred from level 1 to level 2	0	0	0
Fair value liabilities transferred from level 2 to level 1	0	0	0
Fair value assets transferred into level 3	0	0	0
Fair value assets transferred out of level 3	0	0	0
Fair value liabilities transferred into level 3	0	0	0
Fair value liabilities transferred out of level 3	$ 0	$ 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	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		Sep. 30, 2021	Dec. 31, 2020
Assets:
Investments, Fair Value		$ 206,267
Fair Value, Recurring
Assets:
Cash and cash equivalents, Amortized Cost		112,044
Cash and cash equivalents, Fair Value		112,044
Investments, Amortized Cost		206,279
Investments, Gross Unrealized Gains		12
Investments, Gross Unrealized Losses		(24)
Investments, Fair Value		206,267
Total assets measured at fair value, Amortized Cost		318,323	$ 386,200
Total assets measured at fair value, Gross Unrealized Gains		12
Total assets measured at fair value, Gross Unrealized Losses		(24)
Total assets measured at fair value, Fair Value		318,311	386,200
Fair Value, Recurring | Cash | Level 1
Assets:
Cash and cash equivalents, Amortized Cost		52,611	4,788
Cash and cash equivalents, Fair Value		52,611	4,788
Fair Value, Recurring | Money Market Funds | Level 1
Assets:
Cash and cash equivalents, Amortized Cost	[1]	51,183	381,412
Cash and cash equivalents, Fair Value	[1]	51,183	$ 381,412
Fair Value, Recurring | Commercial Paper | Level 2
Assets:
Cash and cash equivalents, Amortized Cost	[1]	8,250
Cash and cash equivalents, Fair Value	[1]	8,250
Fair Value, Recurring | U.S. Government Agency Securities | Level 2
Assets:
Investments, Amortized Cost		24,752
Investments, Gross Unrealized Gains		1
Investments, Fair Value		24,753
Fair Value, Recurring | U.S. Treasury Securities | Level 1
Assets:
Investments, Amortized Cost		43,390
Investments, Gross Unrealized Gains		11
Investments, Fair Value		43,401
Fair Value, Recurring | Corporate Debt | Level 2
Assets:
Investments, Amortized Cost		54,213
Investments, Gross Unrealized Losses		(16)
Investments, Fair Value		54,197
Fair Value, Recurring | Asset-backed Securities | Level 2
Assets:
Investments, Amortized Cost		13,958
Investments, Gross Unrealized Losses		(7)
Investments, Fair Value		13,951
Fair Value, Recurring | Commercial Paper, Not Included with Cash and Cash Equivalents | Level 2
Assets:
Investments, Amortized Cost		69,966
Investments, Gross Unrealized Losses		(1)
Investments, Fair Value		$ 69,965
[1]	Included within cash and cash equivalents on the condensed balance sheets.

Fair Value Measurements and F_5

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Contractual Maturities of Investments (Details) $ in Thousands	Sep. 30, 2021USD ($)
Fair Value Disclosures [Abstract]
Due in less than one year	$ 166,532
Due in one to five years	39,735
Total	$ 206,267

Balance Sheet Details - Schedul

Balance Sheet Details - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 12,045	$ 7,369
Less: accumulated depreciation and amortization	(5,419)	(4,097)
Property and equipment, net	6,626	3,272
Furniture and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	1,217	397
Computers and Computer Software
Property Plant And Equipment [Line Items]
Total property and equipment	111	111
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	8,814	4,739
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,903	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 ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 0.5	$ 0.3	$ 1.3	$ 1.1

Balance Sheet Details - Sched_2

Balance Sheet Details - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Liabilities Current [Abstract]
Preclinical studies	$ 6,335	$ 2,844
Professional fees	643	490
Other accrued expenses	5,049	432
Total	$ 12,027	$ 3,766

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	1 Months Ended				3 Months Ended		9 Months Ended
	Jan. 31, 2021RenewalOption	Nov. 30, 2020	Jul. 31, 2019	Jul. 31, 2016RenewalOption	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)Lease	Sep. 30, 2020USD ($)	Jan. 01, 2021USD ($)
Lessee Lease Description [Line Items]
Operating lease, ROU assets					$ 307		$ 307		$ 900
Operating lease liabilities					1,166		$ 1,166		900
Number of operating lease | Lease							2
Operating leases, rent expense recognized					1,000	$ 200	$ 1,900	$ 500
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 current 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
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, agreement term	48 months
Operating lease, commencement date	Jan. 22, 2021
Operating lease, renewal term	60 months
Operating lease, rent commencement date	Jan. 21, 2022
Number of renewal options | RenewalOption	2
Palo Alto
Lessee Lease Description [Line Items]
Operating lease, ROU assets					300		$ 300
Operating lease liabilities					$ 300		$ 300

Leases - Schedule of Informatio

Leases - Schedule of Information Related to ROU Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Jan. 01, 2021
Leases [Abstract]
Cash paid for operating lease liabilities	$ 920
Operating lease right-of-use assets	307	$ 900
Current operating lease liabilities	613
Non-current operating lease liabilities	553
Total lease liabilities	$ 1,166	$ 900
Weighted-average remaining lease term (in years)	3 months 25 days
Weighted-average discount rate	7.20%

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jan. 01, 2021	Dec. 31, 2020
Leases [Abstract]
Remainder of 2021	$ (253)
2022	487		$ 742
2023	379		190
2024	388
2025	398
Total future undiscounted lease payments	1,399		$ 932
Less: Imputed interest	(233)
Operating lease liabilities	$ 1,166	$ 900

Leases - Schedule of Maturiti_2

Leases - Schedule of Maturities of Lease Liabilities (Parenthetical) (Details) $ in Millions	Sep. 30, 2021USD ($)
Palo Alto
Lessee Lease Description [Line Items]
lease incentives	$ 0.9

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - Lonza DMSA - USD ($)	Jun. 30, 2018	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
Maximum
Loss Contingencies [Line Items]
Payments in equity, percentage	25.00%
Payments in equity, amount	$ 2,500,000
Equity payment, upper limit	$ 10,000,000

Redeemable Convertible Prefer_2

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

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 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	52,587,855	51,071,593
Common stock, shares outstanding	52,587,855	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	$ 7,108,000
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	498,502
Average price	$ 25.15
Aggregate gross proceeds from issuance of common stock	$ 12,500,000
Proceeds from issuance of stock, net of commission and offering expenses	12,200,000
ATM Sales Agreement | Jefferies LLC | Prepaid Expenses and Other Current Assets
Class Of Stock [Line Items]
Receivables	$ 5,000,000
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	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock reserved for future issuances	11,748,083	9,839,680
Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuances	5,427,007	5,188,531
Shares Available for Future Stock Option Grants
Class Of Stock [Line Items]
Common stock reserved for future issuances	6,321,076	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, 2021	Jun. 11, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	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			8,337			8,337		15,056
Options granted						62,382
Exercise of stock options (in shares)			125,583	67,792		578,194	263,626
Weighted-average price per share			$ 3.91	$ 1.60		$ 2.50	$ 1.86
Weighted-average grant date fair value of options granted			$ 17	$ 29.83		$ 14.37	$ 8.17
Intrinsic value of the stock options exercised			$ 2.5	$ 2.5		$ 12.4	$ 5.1
Performance-based Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense					$ 0.3		$ 0.3
Performance-based Awards | IPO
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares vested					362,935		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%
Available for issuance of shares increased	2,553,579
Aggregate number of shares available for issuance			6,321,076			6,321,076
Number of shares outstanding			1,465,620			1,465,620
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding			3,961,387			3,961,387
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%
Available for issuance of shares increased	510,715
Aggregate number of shares available for issuance			1,097,964			1,097,964
Percentage of payroll deductions of eligible compensation		15.00%
Employees purchase shares of common stock of lower of fair market value		85.00%
Offering period		2 years
Purchase period		6 months
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		$ 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%
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%

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of Activity Under Stock Option Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 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	$ 3.91	$ 1.60	$ 2.50	$ 1.86
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
Options Available for Grant, Additional shares authorized			2,553,579
Options Available for Grant, granted			(1,378,321)
Options Available for Grant, forfeited			494,669
Options Available for Grant, Ending Balance	6,321,076		6,321,076
Number of Options, Beginning Balance			5,121,549
Number of Options, granted			1,378,321
Number of Options, exercised			(578,194)
Number of Options, forfeited			(494,669)
Number of Options, Ending Balance	5,427,007		5,427,007
Number of Options, Vested and expected to vest	5,427,007		5,427,007
Number of Options, Exercisable	2,646,355		2,646,355
Weighted-Average Exercise Price Per Share, Beginning Balance			$ 4.99
Weighted-Average Exercise Price Per Share, Options granted			21.46
Weighted-Average Exercise Price Per Share, Options exercised			2.50
Weighted-Average Exercise Price Per Share, Options forfeited			16.53
Weighted-Average Exercise Price Per Share, Ending Balance	$ 8.39		8.39
Weighted-Average Exercise Price Per Share, Vested and expected to vest	8.39		8.39
Weighted-Average Exercise Price Per Share, Exercisable	$ 4.03		$ 4.03
Weighted-Average Remaining Contractual Term (Years)			7 years 8 months 15 days
Weighted-Average Remaining Contractual Term (Years), Vested and expected to vest			7 years 8 months 15 days
Weighted-Average Remaining Contractual Term (Years), Exercisable			6 years 7 months 2 days
Aggregate Intrinsic Value	$ 93,459		$ 93,459
Aggregate Intrinsic Value, Vested and expected to vest	93,459		93,459
Aggregate Intrinsic Value, Exercisable	$ 56,584		$ 56,584

Equity Incentive Plans - Summ_2

Equity Incentive Plans - Summary of Estimated Fair Value of Employee Stock Options (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assumptions
Expected volatility, Minimum	81.20%	93.00%	81.00%	81.20%
Expected volatility, Maximum	81.80%	93.50%	82.50%	93.50%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	5 years 4 months 24 days	5 years 7 months 6 days
Risk-free interest rate		0.30%
Risk-free interest rate, Minimum	0.80%		0.50%	0.30%
Risk-free interest rate, Maximum	1.10%		1.10%	1.40%
Minimum
Fair Value Assumptions
Expected term (in years)			5 years 4 months 24 days	5 years 7 months 6 days
Maximum
Fair Value Assumptions
Expected term (in years)			5 years 6 months	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)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assumptions
Expected volatility, Minimum	81.20%	93.00%	81.00%	81.20%
Expected volatility, Maximum	81.80%	93.50%	82.50%	93.50%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	5 years 4 months 24 days	5 years 7 months 6 days
Risk-free interest rate		0.30%
Risk-free interest rate, Minimum	0.80%		0.50%	0.30%
Risk-free interest rate, Maximum	1.10%		1.10%	1.40%
Minimum
Fair Value Assumptions
Expected term (in years)			5 years 4 months 24 days	5 years 7 months 6 days
Maximum
Fair Value Assumptions
Expected term (in years)			5 years 6 months	6 years 1 month 6 days
2020 Employee Stock Purchase Plan
Fair Value Assumptions
Expected volatility, Minimum	79.60%	109.70%	79.60%	107.00%
Expected volatility, Maximum	88.80%	158.20%	126.30%	158.20%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Risk-free interest rate		0.20%		0.20%
Risk-free interest rate, Minimum	0.00%		0.00%
Risk-free interest rate, Maximum	0.20%		0.20%
2020 Employee Stock Purchase Plan | Minimum
Fair Value Assumptions
Expected term (in years)	6 months	4 months 24 days	6 months	4 months 24 days
2020 Employee Stock Purchase Plan | Maximum
Fair Value Assumptions
Expected term (in years)	2 years	1 year 10 months 24 days	2 years	1 year 10 months 24 days

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	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,937	$ 1,838	$ 7,571	$ 3,499
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	1,023	558	2,688	1,081
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,914	$ 1,280	$ 4,883	$ 2,418

Funding Arrangement - Additiona

Funding Arrangement - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Apr. 30, 2021	Jul. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Aug. 04, 2021	Dec. 31, 2020	Jul. 31, 2020
Funding Arrangement [Line Items]
Grant income			$ 299,000	$ 787,000	$ 677,000	$ 2,152,000
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			300,000	$ 800,000	700,000	$ 2,200,000
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			$ 700,000		$ 700,000			$ 300,000
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	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss (in thousands)	$ (26,615)	$ (21,018)	$ (71,514)	$ (68,480)
Weighted-average shares outstanding used in computing net loss per share, basic and diluted	52,187,303	50,895,358	51,627,249	22,354,212
Net loss per share, basic and diluted	$ (0.51)	$ (0.41)	$ (1.39)	$ (3.06)

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	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
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	5,489,389	5,094,669	5,489,389	5,094,669

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Tax provision	$ 0	$ 0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	May 29, 2018	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Common stock, shares owned		52,587,855		52,587,855		51,071,593
Warrant exercised							46,869
Change in fair value of redeemable convertible preferred stock warrant					$ 179,000
Sutro Biopharma, Inc
Related Party Transaction [Line Items]
Common stock, shares owned		1,600,000		1,600,000		1,600,000
Accrued expenses payable		$ 0		$ 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%		4.00%
Percentage of royalty payment on net sales of vaccine compositions for animal health		2.00%		2.00%
Sutro Biopharma, Inc | Supply Agreement
Related Party Transaction [Line Items]
Expenses related to agreement		$ 0	$ 100,000	$ 2,400,000	300,000
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	$ 0	$ 0	$ 200,000