Vaxcyte (PCVX) 10-Q 9 May 22 2022 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2022	May 05, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Entity Registrant Name	VAXCYTE, INC.
Entity Central Index Key	0001649094
Current Fiscal Year End Date	--12-31
Entity Emerging Growth Company	false
Entity File Number	001-39323
Entity Tax Identification Number	46-4233385
Entity Address, Address Line One	825 Industrial Road
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	San Carlos
Entity Address, State or Province	CA
Entity Incorporation, State or Country Code	DE
Entity Address, Postal Zip Code	94070
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		58,313,828
Entity Filer Category	Large 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	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 201,741	$ 68,985
Short-term investments	132,900	176,985
Prepaid expenses and other current assets	7,582	10,378
Total current assets	342,223	256,348
Property and equipment, net	10,138	7,954
Operating lease right-of-use assets	26,121	27,958
Long-term investments	17,697	27,117
Restricted cash	871	871
Other assets	5,667	4,089
Total noncurrent assets	60,494	67,989
Total assets	402,717	324,337
Current liabilities:
Accounts payable	4,801	6,758
Accrued compensation	1,270	3,455
Accrued manufacturing expenses	6,856	4,440
Accrued expenses	7,744	8,787
Operating lease liabilities — current	6,578	5,276
Total current liabilities	27,249	28,716
Operating lease liabilities — long-term	15,832	11,507
Other liabilities	93	96
Total liabilities	43,174	40,319
Commitments and contingencies (Note 6)
Stockholders' Equity
Preferred stock, $0.001 par value 10,000,000 shares authorized at March 31, 2022 and December 31, 2021; no shares issued and outstanding at March 31, 2022 and December 31, 2021	0	0
Common stock, $0.001 par value 500,000,000 shares authorized at March 31, 2022 and December 31, 2021; 56,499,544 and 53,031,978 shares issued and outstanding at March 31, 2022 and December 31, 2021, respectively	59	56
Additional paid-in capital	697,944	582,844
Accumulated other comprehensive loss	(833)	(241)
Accumulated deficit	(337,627)	(298,641)
Total stockholders' equity	359,543	284,018
Total liabilities and stockholders' equity	$ 402,717	$ 324,337

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Mar. 31, 2022	Dec. 31, 2021
Statement Of Financial Position [Abstract]
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	56,499,544	53,031,978
Common stock, shares outstanding	56,499,544	53,031,978

Condensed Statements of Operati

Condensed Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating expenses:
Research and development (including related party expenses of $0 and $1,612 for the three months ended March 31, 2022 and 2021, respectively	$ 31,678	$ 17,258
General and administrative	7,543	5,885
Total operating expenses	39,221	23,143
Loss from operations	(39,221)	(23,143)
Other income (expense), net:
Interest income	134	61
Grant income	160
Realized loss on marketable securities	(65)
Foreign currency transaction gains	6	1,862
Total other income (expense), net	235	1,923
Net loss	$ (38,986)	$ (21,220)
Net loss per share, basic and diluted	$ (0.68)	$ (0.41)
Weighted-average shares outstanding, basic and diluted	57,547,808	51,174,978

Condensed Statements of Opera_2

Condensed Statements of Operations (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Research and development expense to related party	$ 0	$ 1,612

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement Of Income And Comprehensive Income [Abstract]
Net Loss	$ (38,986)	$ (21,220)
Other comprehensive loss:
Unrealized losses on investments	(592)	(47)
Comprehensive loss	$ (39,578)	$ (21,267)

Condensed Statements of Redeema

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Follow on public offering	Follow on public offeringCommon Stock	Follow on public offeringAdditional Paid-in Capital	At the market offering	At the market offeringCommon Stock	At the market offeringAdditional Paid-in Capital
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
Issuance of common stock in connection follow-on public offering, net of issuance costs									$ 3,098
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs									$ 3,098
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, 2021	284,018	$ 56	582,844	(298,641)	(241)
Beginning balance, shares at Dec. 31, 2021		53,031,978
Exercise of stock options	282		282
Exercise of stock options (in shares)		91,044
Vesting of early exercised stock options	2		2
Issuance of common stock in connection follow-on public offering, net of issuance costs						$ 107,622	$ 3	$ 107,619			$ 3,098
Issuance of common stock in connection follow-on public offering, net of issuance costs, shares							3,250,000			126,522
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs						$ 107,622	$ 3	$ 107,619			$ 3,098
Issuance of common stock upon initial public offering or at-the-market offering, net of issuance costs (in shares)							3,250,000			126,522
Stock-based compensation expense	4,099		4,099
Unrealized gains (losses) on investments	(592)				(592)
Net Loss	(38,986)			(38,986)
Ending balance at Mar. 31, 2022	$ 359,543	$ 59	$ 697,944	$ (337,627)	$ (833)
Ending balance, shares at Mar. 31, 2022		56,499,544

Condensed Statements of Redee_2

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2022USD ($)
Issuance costs	$ 7,376
Common Stock | At the market offering
Issuance costs	$ 114

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net loss	$ (38,986)	$ (21,220)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	582	347
Stock-based compensation expense	4,099	1,865
Amortization of operating right-of-use assets	1,787	180
Net amortization of premiums on investments	321	151
Loss on disposal of fixed assets	44
Asset impairment charges	57
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	2,791	(557)
Other assets	(1,577)	(441)
Operating lease liabilities	5,619	(105)
Accounts payable	(1,933)	2,185
Accrued compensation	(2,185)	723
Accrued manufacturing expenses	2,416	2,525
Accrued expenses	(737)	1,142
Net cash used in operating activities	(27,702)	(13,205)
Cash flows from investing activities:
Purchases of property and equipment	(2,920)	(1,246)
Proceeds from sale of property and equipment	7
Purchases of investments	(6,972)	(172,145)
Maturities of investments	59,551
Net cash provided by (used in) investing activities	49,666	(173,391)
Cash flows from financing activities:
Proceeds from follow-on public offering, net of underwriters' commissions and discounts	107,622
Proceeds from exercise of common stock options	282	487
Proceeds from issuance of common stock related to at-the-market offering, net of issuance costs	3,115
Net cash provided by financing activities	111,019	487
Effect of exchange rate changes on cash and cash equivalents	(227)	(281)
Net increase (decrease) in cash, cash equivalents and restricted cash	132,756	(186,390)
Cash, cash equivalents and restricted cash, beginning of period	69,856	386,200
Cash, cash equivalents and restricted cash, end of period	202,612	199,810
Supplemental disclosures of non-cash investing and financing activities:
Purchases of property and equipment recorded in accounts payable and accrued expenses	664	$ 1,537
Deferred offering costs included in accounts payable and accrued expenses	$ 23

Company Organization and Nature

Company Organization and Nature of Business	3 Months Ended
	Mar. 31, 2022
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Company Organization and Nature of Business	1. Company Organization and Nature of Business Vaxcyte, Inc. (“we,” “us,” “the Company,” or “Vaxcyte”), headquartered in San Carlos, California, was incorporated in the state of Delaware on November 27, 2013 as SutroVax, Inc. and we changed our name to Vaxcyte, Inc. on May 15, 2020. We are a clinical-stage vaccine innovation company engineering high-fidelity vaccines to protect humankind from the consequences of bacterial diseases. We are developing broad-spectrum conjugate and novel protein vaccines to prevent or treat bacterial infectious diseases. We are re-engineering the way highly complex vaccines are made through modern synthetic techniques, including advanced chemistry and the XpressCF cell-free protein synthesis platform, exclusively licensed from Sutro Biopharma, Inc. Unlike conventional cell-based approaches, our system for producing difficult-to-make proteins and antigens is intended to accelerate our ability to efficiently create and deliver high-fidelity vaccines with enhanced immunological benefits. Our pipeline includes pneumococcal conjugate vaccine ("PCV") candidates that we believe are among the most broad-spectrum PCV candidates currently in development, targeting the approximately $ 7 billion global pneumococcal vaccine market. Our lead vaccine candidate, VAX-24, is a 24-valent broad-spectrum investigational PCV being developed for the prevention of invasive pneumococcal disease ("IPD") and pneumonia. On January 6, 2022, we announced that the U.S. Food and Drug Administration ("FDA"), cleared our investigational new drug ("IND") application for VAX-24 in adults. On February 23, 2022, we announced the initiation of our Phase 1/2 clinical proof-of-concept study in adults 18 to 64 years of age. The Phase 1 portion of the study includes 64 healthy adults 18 to 49 years of age and the Phase 2 portion of the study includes approximately 800 healthy adults 50 to 64 years of age. On April 4, 2022, we announced the initiation of the Phase 2 portion of this study in adults 50 to 64 years of age. The initiation of the Phase 2 portion of the study occurred after an independent Data Monitoring Committee completed a prespecified review of Phase 1 safety and tolerability data and recommended that the study progress as planned. We expect to announce topline safety, tolerability and immunogenicity results from the Phase 1 and Phase 2 portions of this study by the end of 2022. Based on the successful completion of the Phase 1 portion of this study, we expect to begin enrollment in a separate Phase 2 study in healthy adults aged 65 and older and to announce topline safety, tolerability and immunogenicity results from this study in the first half of 2023. Subject to a pre-IND meeting with the FDA and the successful topline results of the Phase 1/2 proof-of-concept study in adults 18 to 64 years of age, we anticipate submitting a pediatric IND application to the FDA for VAX-24 in the first half of 2023. Our second PCV candidate, VAX-XP, leverages our scalable and modular platform and builds on the technical proof of concept established by VAX-24 and is designed to expand the breadth of coverage to greater than 30 strains without compromising immunogenicity due to carrier suppression. In addition to our PCV franchise, our pipeline includes VAX-A1, a novel conjugate vaccine candidate designed to prevent Group A Strep; VAX-PG, a novel protein vaccine candidate targeting the keystone pathogen responsible for periodontitis; and other discovery-stage programs. Our primary activities since incorporation have been to perform research and development, undertake preclinical studies and conduct manufacturing activities in support of our product development efforts; organize and staff the Company; establish our intellectual property portfolio; and raise capital to support and expand such activities. Follow-on Offering In January 2022, we completed an underwritten public offering in which we issued 2,500,000 shares of our common stock at a price of $ 20.00 per share, and pre-funded warrants to purchase 2,500,000 shares of our common stock at a price of $ 19.999 per underlying share. In February 2022, the underwriters exercised their option to purchase an additional 750,000 shares of common stock. In aggregate, we received approximately $ 107.6 million in net proceeds after deducting underwriting discounts and commissions and other offering expenses payable by us.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2022
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, or 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 March 31, 2022, the condensed statements of operations, comprehensive loss and stockholders’ equity for the three months ended March 31, 2022 and 2021 and the condensed statements of cash flows for the three months ended March 31, 2022 and 2021 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 months ended March 31, 2022 and 2021 are also unaudited. The results of operations for the three months ended March 31, 2022 are not necessarily indicative of the results to be expected for the year ending December 31, 2022 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, 2021 included in our Annual Report on Form 10-K filed with the SEC on February 28, 2022. 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. Cash, cash equivalents and restricted cash as reported within the condensed balance sheets that total to the same amounts shown in the condensed statement of cash flows as follows: March 31, December 31, 2022 2021 (in thousands) Cash and cash equivalents $ 201,741 $ 68,985 Restricted cash 871 871 Cash, cash equivalents and restricted cash $ 202,612 $ 69,856 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 loss. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income (expense), net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income (expense), net. We evaluate securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are included in other income (expense), net. We classify our investments as short or long term primarily based on the remaining contractual maturity of the securities. 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, including pre-funded warrants issued, during the period, without consideration for common stock equivalents. Shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing net loss per share because the shares may be issued for little consideration, are fully vested and are exercisable after the original issuance date. 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 March 31, 2022 and December 31, 2021 , we recorded deferred offering costs of $ 0.5 million and $ 0.5 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) and its associated amendments (“ASC 842”), we determine if an arrangement is a lease at inception. In addition, we determine whether a lease meets the classification criteria of a finance or operating lease at the lease commencement date considering whether: (i) the lease transfers ownership of the underlying asset to the lessee at the end of the lease term; (ii) the lease grants the lessee an option to purchase the underlying asset that the lessee is reasonably certain to exercise; (iii) the lease term is for a major part of the remaining economic life of the underlying asset; (iv) the present value of the sum of the lease payments and residual value guaranteed by the lessee equals or exceeds substantially all of the fair value of the underlying asset; and (v) the underlying asset is such a specialized nature that it is expected to have no alternative use to the lessor at the end of the lease term. As of March 31, 2022 , our lease population consisted of real estate operating leases. As of March 31, 2022, we did no t have finance leases. Operating leases are included in Operating lease right-of-use ("ROU") assets, Operating lease liabilities — current and Operating lease liabilities — long term in our condensed balance sheet. ROU assets represent our right to use the underlying assets for the lease term and lease liabilities represent our obligation to make lease payments arising from the leases. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, if the rate implicit in the lease is not readily determinable, we use our incremental borrowing rate based on the information available at the lease commencement date. We determine the incremental borrowing rate based on an analysis of corporate bond yields with a credit rating similar to us. The determination of our incremental borrowing rate requires management judgment, including development of a synthetic credit rating and cost of debt, as we currently do not carry any debt. We believe that the estimates used in determining the incremental borrowing rate are reasonable based upon current facts and circumstances. Applying different judgment to the same facts and circumstances could yield a different incremental borrowing rate. The operating lease ROU assets also include adjustments for prepayments and accrued lease payments and exclude lease incentives. ROU assets and lease liabilities may include options to extend or terminate leases if it is reasonably certain that we will exercise such options. Lease payments which are fixed and determinable are amortized as rent and lease expense on a straight-line basis over the expected lease term. Variable lease costs, which are dependent on usage, a rate or index, including common area maintenance charges, are expensed as incurred. Lease agreements that include lease and non-lease components are accounted for as a single lease component. Lease agreements with non-cancelable terms of less than 12 months are not recorded on our condensed balance sheets. 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. R ecently Adopted Accounting Pronouncements In November 2021, the FASB issued ASU 2021-10, Government Assistance (Topic 832): Disclosure by Business Entities about Government Assistance , which requires disclosures about transactions with a government entity that are accounted for by applying a grant or contribution accounting model by analogy to other accounting guidance, such as a grant model within International Accounting Standard 20, Accounting for Government Grants and Disclosure of Government Assistance (Subtopic 958-605), Not-For-Profit Entities - Revenue Recognition . The required disclosures include (i) the nature of the transaction and the related accounting policy used to account for the transaction, (ii) the financial statement line items that are affected by the transactions and (iii) the significant terms and conditions of the transactions, including commitments and contingencies. This standard is effective for annual periods beginning after December 15, 2021, with early adoption and retrospective or prospective application permitted. This standard is effective for us on January 1, 2022 and only impacts annual financial statement footnote disclosures. In Note 10, "Funding Arrangement," we included disclosures on our cost-reimbursement research award from Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator ("CARB-X"). The adoption of this standard did not have a material impact on our financial statements. Recently Issued Accounting Pronouncements – Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments and has subsequently issued related amendments, collectively referred to as “Topic 326.” Topic 326 requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. We are currently assessing the impact of this standard to our financial statements and related disclosures.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2022
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 upon the sale of an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance also establishes a three-level valuation hierarchy that prioritizes the inputs to valuation techniques used to measure fair value based upon whether such inputs are observable or unobservable. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect market assumptions made by the reporting entity. The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows: Level 1— Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2— Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 — Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. Level 1 securities consist of highly liquid money market funds for which the carrying amounts approximate their fair values due to their short maturities. U.S. Treasury securities are valued using Level 1 inputs based on unadjusted, quoted prices in active markets that are observable at the measurement date for identical assets or liabilities. Level 2 securities, consisting of corporate debt, commercial paper, U.S. government agency securities and asset-backed securities, are measured based on other observable inputs, including broker or dealer quotations or alternative pricing sources. When quoted prices in active markets for identical assets or liabilities are not available, we rely on non-binding quotes from our investment managers, which are based on proprietary valuation models of independent pricing services. These models generally use inputs such as observable market data, quoted market prices for similar instruments or historical pricing trends of securities relative to our peers. To validate the fair value determinations provided by our investment managers, we review the pricing movement in the context of overall market trends and trading information from our investment managers. In addition, we assess the inputs and methods used in determining the fair value in order to determine the classification of securities in the fair value hierarchy. We had no Level 3 securities as of March 31, 2022 or December 31, 2021. There were no transfers within the hierarchies during the three months ended March 31, 2 0 22 or the year ended December 31, 2 0 21. The following tables set forth our financial instruments measured at fair value on a recurring basis by level within the fair value hierarchy at March 31, 2022 and December 31, 2021: March 31, 2022 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 140,164 $ — $ — $ 140,164 Money market funds Level 1 23,104 — — 23,104 U.S. Treasury securities Level 1 3,000 3,000 Commercial paper Level 2 35,476 — ( 3 ) 35,473 Total cash and cash equivalents 201,744 — ( 3 ) 201,741 Investments: U.S. Treasury securities Level 1 45,191 — ( 266 ) 44,925 Commercial paper Level 2 42,940 — ( 46 ) 42,894 Corporate debt Level 2 24,779 — ( 271 ) 24,508 Asset-backed securities Level 2 13,840 — ( 62 ) 13,778 U.S. government agency securities Level 2 24,677 — ( 185 ) 24,492 Total investments 151,427 — ( 830 ) 150,597 Total assets measured at fair value $ 353,171 $ — $ ( 833 ) $ 352,338 December 31, 2021 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 27,834 $ — $ — $ 27,834 Money market funds Level 1 17,555 — — 17,555 Commercial paper Level 2 23,597 — ( 1 ) 23,596 Total cash and cash equivalents 68,986 — ( 1 ) 68,985 Investments: U.S. Treasury securities Level 1 45,290 — ( 73 ) 45,217 Commercial paper Level 2 61,941 — ( 22 ) 61,919 Corporate debt Level 2 58,498 — ( 74 ) 58,424 Asset-backed securities Level 2 13,899 — ( 25 ) 13,874 U.S. government agency securities Level 2 24,714 — ( 46 ) 24,668 Total investments 204,342 — ( 240 ) 204,102 Total assets measured at fair value $ 273,328 $ — $ ( 241 ) $ 273,087 The following table presents the contractual maturities of our investments as of March 31, 2022 (in thousands): March 31, 2022 Fair Value Due in less than one year $ 132,900 Due in one to five years 17,697 Total $ 150,597

Balance Sheet Details

Balance Sheet Details	3 Months Ended
	Mar. 31, 2022
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 March 31, 2022 and December 31, 2021 consisted of the following: March 31, December 31, 2022 2021 (in thousands) Furniture and equipment $ 1,608 $ 1,619 Computers and computer software 439 430 Lab equipment 10,883 9,453 Leasehold improvements 1,329 — Total property and equipment 14,259 11,502 Less: accumulated depreciation and amortization ( 4,121 ) ( 3,548 ) Property and equipment, net $ 10,138 $ 7,954 Depreciation and amortization expense for the three months ended March 31, 2022 and 2021 was $ 0.6 million and $ 0.3 million, respectively. Accrued Expenses Accrued expenses as of March 31, 2022 and December 31, 2021 consisted of the following: March 31, December 31, 2022 2021 (in thousands) Preclinical studies $ 5,327 $ 5,039 Clinical studies 475 — Professional fees 972 400 Other accrued expenses 970 3,348 Total $ 7,744 $ 8,787

Leases

Leases	3 Months Ended
	Mar. 31, 2022
Leases [Abstract]
Leases	5. Leases Operating Lease Obligations 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 . In July 2019, we leased another facility in Foster City, California as a result of growth in personnel and lab space requirements. The original term of this lease was from July 1, 2019 to October 31, 2021 , with no renewal options . In November 2020, we extended the terms of both of these leases for six months to March 1, 2022 and April 30, 2022 , respectively. In February 2022, we entered into an early termination agreement for one of the facilities in Foster City and terminated our lease on February 12, 2022 instead of April 30, 2022. In January 2021, we entered into a lease agreement for our new corporate headquarters facility 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 expires December 31, 2025 . We have two 60 -month renewal options. The original term of the license agreement for the temporary space in Palo Alto terminated when the San Carlos office leasehold improvements were completed and we moved into our new corporate headquarters. We extended the license agreement for the Palo Alto office by 60 days to March 3, 2022 to accommodate our relocation plan. These two leases are accounted for as a combined lease because the contracts were negotiated as a package with the same commercial objective. Information related to our ROU assets and related lease liabilities was as follows (dollar amounts in thousands): March 31, 2022 Cash paid for operating lease liabilities $ 621 Operating lease right-of-use assets 26,121 Current operating lease liabilities $ 6,578 Non-current operating lease liabilities 15,832 Total lease liabilities $ 22,410 Weighted-average remaining lease term (in years) 3.54 Weighted-average discount rate 7.6 % Maturities of lease liabilities as of March 31, 2022 were as follows: Years ending December 31, (in thousands) Remainder of 2022 $ 5,132 2023 6,639 2024 6,805 2025 6,977 Thereafter — Total future undiscounted lease payments 25,553 Less: Imputed interest ( 3,143 ) Total lease liabilities $ 22,410 Future minimum payments required under operating leases as of December 31, 2021 were as follows: Years ending December 31, (in thousands) 2022 (1) $ ( 105 ) 2023 6,639 2024 6,805 2025 6,976 Thereafter — Total future undiscounted lease payments 20,315 Less: Imputed interest ( 3,532 ) Total lease liabilities $ 16,783 (1) Maturities for 2022 are net of lease incentives of $ 0.9 million allocated to the Palo Alto office. Rent expense recognized under the leases was $ 2.2 million and $ 0.4 million for the three months ended March 31, 2022 and 2021 , respectively.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2022
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 March 31, 2022, 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. 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. In April 2022, we entered into a master services agreement for drug product development and manufacturing (the "Master Services Agreement") with Lonza effective as of March 22, 2022, pursuant to which Lonza will perform manufacturing process development and clinical manufacture and supply of our proprietary pneumococcal conjugate vaccine. Unless terminated earlier, the Master Services Agreement will remain in place for a period of five years. Either party may terminate the Master Services Agreement for any reason with prior written notice to the other party, provided that Lonza may not exercise such right until a specified future date. In addition, either party may terminate the Master Services Agreement (i) within a given time period upon any material breach that is left uncured by the other party, or (ii) immediately if the other party becomes insolvent. We may also terminate the Master Services Agreement upon an extended force majeure event. Upon expiration and/or termination of the Master Services Agreement and/or any purchase order, we will pay Lonza for all services rendered, all costs incurred, all unreimbursed capital equipment and any cancellation fees. Under the Lonza Agreements, we will pay Lonza agreed-upon fees for Lonza’s performance of manufacturing services and reimburse Lonza for its out-of-pocket costs for purchases of raw materials, as well as a customary procurement and 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.

Common Stock

Common Stock	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Common Stock	7. 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 56,499,544 and 53,031,978 shares were issued and outstanding as of March 31, 2022 and December 31, 2021, 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 March 31, 2022 and December 31, 2021 , 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 (the “ATM Sales Agreement”) with Jefferies LLC (“Jefferies”), which provides that, upon the terms and subject to the conditions and limitations set forth in the ATM Sales Agreement, we may elect to issue and sell, from time to time, shares of our common stock having an aggregate offering price of up to $ 150.0 million through Jefferies acting as our sales agent or principal. We will pay Jefferies a commission of up to 3.0 % of the gross sales proceeds of any common stock sold through Jefferies under the ATM Sales Agreement; however, we are not obligated to make any sales of common stock. As of March 31, 2022 , we have sold 693,567 shares of our common stock under the ATM Sales Agreement at an average price of $ 25.29 per share for aggregate gross proceeds of $ 17.5 million ($ 17.0 million net of commissions and offering expenses). In January 2022, we completed an underwritten public offering in which we issued 2,500,000 shares of common stock at a price of $ 20.00 per share and pre-funded warrants to purchase 2,500,000 shares of our common stock at a price of $ 19.999 per underlying share. In February 2022, t he underwriters exercised their option to purchase an additional 750,000 shares of common stock. In aggregate, we received approximately $ 107.6 million in net proceeds after deducting underwriting discounts and commissions and other offering expenses payable by us. 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: March 31, December 31, 2022 2021 Options issued and outstanding 6,797,419 5,295,007 Restricted stock units outstanding 373,441 — Shares available for future stock option grants 6,789,842 6,104,756 Total 13,960,702 11,399,763

Pre-Funded Warrants

Pre-Funded Warrants	3 Months Ended
	Mar. 31, 2022
Equity [Abstract]
Pre-Funded Warrants	8. P re-Funded Warrants In connection with our underwritten public offering in January 2022, we issued 2,500,000 shares of our common stock at a price of $ 20.00 per share and pre-funded warrants to purchase 2,500,000 shares of our common stock at a price of $ 19.999 per underlying share. Each pre-funded warrant has an exercise price of $ 0.001 per share. The public offering price for the pre-funded warrants was equal to the public offering price of our common stock, less the $ 0.001 exercise price of each pre-funded warrant and was recorded as a component of stockholders' equity within additional paid-in-capital. The pre-funded warrants will not expire until they are fully exercised. The pre-funded warrants will be exercisable, at the option of each holder, in whole or in part by delivering to us a duly executed exercise notice and payment of the exercise price. No fractional shares of common stock will be issued in connection with the exercise of a pre-funded warrant. The holder of the pre-funded warrants may also satisfy its obligation to pay the exercise price through a "cashless exercise," in which the holder receives the net value of the pre-funded warrant in shares of common stock determined according to the formula set forth in the pre-funded warrant. The pre-funded warrants will not expire until they are fully exercised. However, we may not effect the exercise of any pre-funded warrants, and a holder will not be entitled to exercise any portion of any pre-funded warrants that, upon giving effect to such exercise, would cause: (i) the aggregate number of shares of our common stock beneficially owned by such holder (together with affiliates) to exceed 9.99 % of the number of shares of our common stock outstanding immediately after giving effect to the exercise; or (ii) the combined voting power of our securities beneficially owned by such holder (together with its affiliates) to exceed 9.99 % of the combined voting power of all of our securities outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the pre-funded warrants. However, any holder of a pre-funded warrant may increase or decrease such percentage to any other percentage not in excess of 19.99 % upon at least 61 days' prior notice for the holder to us. As of March 31, 2022, no shares underlying the pre-funded warrants had been exercised.

Equity Incentive Plans

Equity Incentive Plans	3 Months Ended
	Mar. 31, 2022
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plans	9. 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 ("RSUs") 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. Our RSUs granted to new employees generally vest over four years at a rate of 25 % upon one year from the grant date, then 12.5 % every six months thereafter. Our other RSUs granted to employees generally vest over three and a half years at a rate of 25 % upon six months from the grant date, then 12.5 % every six months thereafter. 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 term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount equal to 5 % of the outstanding number of shares of our common stock on December 31 of the preceding calendar year or such lesser amount as determined by our board of directors. Effective January 1, 2022, the number of shares of common stock available under the 2020 Plan increased by 2,651,598 shares pursuant to the evergreen provision. As of March 31, 2022, an aggregate of 7,162,898 shares of common stock were available for issuance under the 2020 Plan. Our 2014 Plan permitted the granting of incentive stock options, non-statutory stock options, restricted stock and other stock-based awards. Subsequent to the adoption of the 2020 Plan, no additional equity awards can be made under the 2014 Plan. As of March 31, 2022, 3,568,919 shares and 3,228,500 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 March 31, 2022 and December 31, 2021 , 6,484 and 7,410 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 March 31, 2022 and December 31, 2021 were both less than $ 0.1 million and were recorded in other liabilities. Stock Option Activity Stock option a ctivity under our 2020 Plan and 2014 Plan, which excludes options to purchase 62,382 shares granted outside of the 2020 Plan and 2014 Plan, was as follows: Options Outstanding Stock Option Activity Options Number Weighted- Weighted- Aggregate Balances — December 31, 2021 6,104,756 5,295,007 $ 9.30 Additional shares authorized 2,651,598 — Options granted ( 1,605,819 ) 1,605,819 $ 24.57 Options exercised — ( 91,044 ) $ 3.18 Options forfeited 12,363 ( 12,363 ) $ 22.16 Balances — March 31, 2022 7,162,898 6,797,419 $ 12.96 8.08 $ 78,759 Vested and expected to vest — March 31, 2022 6,797,419 $ 12.96 8.08 $ 78,759 Exercisable at March 31, 2022 2,828,303 $ 5.35 6.90 $ 53,676 During the three months ended March 31, 2022 and 2021, 91,044 and 267,208 shares of stock options, respectively, were exercised for cash at a weighted-average price per share of $ 3.18 and $ 1.82 , respectively. The weighted-average grant date fair value of options granted for the three months ended March 31, 2022 and 2021 was $ 16.34 and $ 17.70 , respectively. The intrinsic value of the stock options exercised was $ 1.8 million and $ 6.4 million for the three months ended March 31, 2022 and 2021, respectively. Restricted Stock Units Activity In March 2022, our board of directors authorized the issuance of RSUs under our 2020 Plan and adopted a form of Restricted Stock Unit Grant Notice and Restricted Stock Unit Award Agreement ("the RSU Agreement"), which is intended to serve as a standard form agreement for RSU grants issued to employees. RSU activity for the three months ended March 31, 2022 was as follows: Shares Weighted- Unvested at December 31, 2021 — $ — Granted 373,823 24.67 Vested — — Cancelled ( 382 ) 24.79 Unvested at March 31, 2022 373,441 24.67 The weighted-average grant date fair value of RSUs granted during the three months ended March 31, 2022 was $ 24.67 . The aggregate fair value of unvested RSU is calculated using the closing price of our common stock of $ 24.15 on March 31, 2022. As of March 31, 2022, the unrecognized stock-based compensation cost of unvested RSUs was $ 7.0 million, which is expected to be recognized over a weighted-average period of 3.5 years. There were no RSUs vested as of March 31, 2022. 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 purchase periods within the two-year offering period. A total of 650,000 shares of common stock were approved to be initially reserved for issuance under the 2020 ESPP. In addition, the number of shares of common stock available for issuance under the 2020 ESPP will be automatically increased on the first day of each calendar year during the ten-year term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount of 1 % of the outstanding number of shares of our common stock on December 31 st of the preceding calendar year or such lesser amount as determined by our board of directors. Effective January 1, 2022, the number of shares of common stock available under the 2020 ESPP increased by 530,319 shares pursuant to the evergreen provision. As of March 31, 2022 , 1,601,023 shares of common stock were available for issuance under the 2020 ESPP. Stock-based Compensation We estimated the fair value of employee stock options using the Black-Scholes option-pricing model for the three months ended March 31, 2022 and 2021 using the following weighted-average assumptions: Three Months Ended March 31, 2022 2021 Fair Value Assumptions Expected volatility 78.1 % - 78.9 % 81.0 % - 82.5 % Expected dividend yield 0 % 0 % Expected term (in years) 5.4 5.5 Risk-free interest rate 1.6 % - 2.4 % 0.5 % - 1.0 % We estimated the fair value of shares under the 2020 ESPP using the Black-Scholes option-pricing model for the three months ended March 31, 2022 and 2021 using the following weighted-average assumptions: Three Months Ended March 31, 2022 2021 Fair Value Assumptions Expected volatility 86.7 % - 97.5 % 105.8 % - 158.2 % Expected dividend yield 0 % 0 % Expected term (in years) 0.5 - 2.0 0.4 - 2.0 Risk-free interest rate 0.1 % - 0.5 % 0.1 % - 0.2 % We recorded total stock-based compensation expense for the three months ended March 31, 2022 and 2021 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 March 31, 2022 2021 (in thousands) Research and development $ 1,775 $ 683 General and administrative 2,324 1,182 Total $ 4,099 $ 1,865

Funding Arrangement

Funding Arrangement	3 Months Ended
	Mar. 31, 2022
Funding Arrangement [Abstract]
Funding Arrangement	10. Funding Arrangement In July 2019, we received a cost-reimbursement research award from CARB-X, a public-private partnership funded under a Cooperative Agreement from Assistant Secretary for Preparedness and Response/Biomedical Advanced Research and Development Authority (“BARDA”) and by awards from Wellcome Trust, Germany’s Federal Ministry of Education and Research, the United Kingdom Global Antimicrobial Resistance Innovation Fund and the Bill & Melinda Gates Foundation. In connection with this funding, we entered into a cost-reimbursement sub-award agreement with the Trustees of Boston University, the administrator of the program. The initial award provided the potential for funding up to four years to develop a universal vaccine to prevent infections caused by Group A Strep bacteria, which include pharyngitis, impetigo and necrotizing fasciitis. The initial award committed initial funding of up to $ 1.6 million for our VAX-A1 program and, subject to a CARB-X decision to extend the options, up to $ 15.1 million in total funding available upon achievement of development milestones over the next four years . Specified research expenditures are reimbursable expenses associated with agreed-upon activities needed to advance the research project supported by the grant. These expenditures can include labor, laboratory supplies, travel, consulting and third-party vendor research and development support costs. In July 2020, the CARB-X agreement was amended with the initial funding amount increased from $ 1.6 million to $ 2.7 million. In December 2020, we reached the maximum CARB-X funding limit for this initial funding period, and subsequently submitted our funding proposal to CARB-X for the next period under our agreement. In April 2021, we received approval for the next phase of CARB-X development and executed the cost-reimbursement sub-award agreement with the Trustees of Boston University in August 2021. Pursuant to the agreement, the award committed additional funding of $ 3.2 million for IND-enabling activities and total potential funding of up to $ 29.7 million (including the current $ 3.2 million award and the prior $ 2.7 million award) upon the achievement of future VAX-A1 development milestones. In January 2022, CARB-X revised the parameters for the contribution of CARB-X funding and implemented maximum funding levels for all grant recipients. As a result, our total funding available upon achievement of development milestones through Phase 1 human clinical trials was revised from $ 29.7 million to $ 13.9 million. In April 2021, we received a cost-reimbursement research award from 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 $ 0.2 million and $ 0 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 March 31, 2022 and 2021, respectively. A grant receivable of $ 0.1 million and $ 1.2 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 March 31, 2022 and December 31, 2021 , respectively.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2022
Earnings Per Share [Abstract]
Net Loss Per Share	11. 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 2022 2021 Net loss (in thousands) $ ( 38,986 ) $ ( 21,220 ) Weighted-average shares outstanding used in computing net (1) 57,547,808 51,174,978 Net loss per share, basic and diluted $ ( 0.68 ) $ ( 0.41 ) (1) Includes shares of common stock into which pre-funded warrants may be exercised. See Note 8 - Pre-Funded Warrants. Potentially dilutive securities outstanding as of the periods presented below were excluded from the computation of diluted net loss per share for the three months ended March 31, 2022 and 2021 because including them would have been antidilutive: As of March 31, 2022 2021 Stock options 6,859,801 4,863,399 Restricted stock units 373,441 — Total 7,233,242 4,863,399

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	12. 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 months ended March 31, 2022, 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 months ended March 31, 2022 , we reported zero tax provision. We do not have any tax audits or other issues pending.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2022
Related Party Transactions [Abstract]
Related Party Transactions	13. Related Party Transactions We have an ongoing relationship with Sutro Biopharma. 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 a 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 . In connection with the Sutro Biopharma License Agreement, under the Sutro Biopharma Supply Agreement, Sutro Biopharma has agreed to manufacture and supply extracts and reagents for us on a cost-plus basis. In consideration for the rights licensed, we are obligated to pay a 4 % royalty on worldwide aggregate annual net sales of our vaccine products for human health and a 2 % royalty on annual net sales of vaccine products for animal health. In License Amendment A1, the Parties amended the license agreement to remove a pre-IND regulatory meeting as a diligence milestone and to agree that certain other diligence milestones had been satisfied. In License Amendment A2, the Parties amended the license agreement to add certain terms confirming our obligation to purchase Sutro Biopharma’s proprietary extract from E. coli (“Extract”) from Sutro Biopharma. In addition, the Parties amended the license agreement to specify our rights to a transfer of certain know-how relating to the manufacture of Extract in the event of a declaration of bankruptcy by Sutro Biopharma. Finally, the Parties agreed to terms providing for injunctive relief in the event of a breach or threatened breach by the other party. In the Sutro Biopharma Supply Agreement, the Parties agreed to terms for the supply of manufactured Extract and custom reagents by Sutro Biopharma for us to use in manufacturing vaccine compositions in non-clinical research or in Phase 1 or Phase 2 clinical trials. The term of the Sutro Biopharma Supply Agreement is from execution until the later of July 31, 2021 and the date the parties enter into and commence activities under the supply agreement unless extended through a subsequent supply agreement for the supply of Extract and custom reagents for vaccine compositions for Phase 3 and commercial uses as contemplated in the Supply Agreement. In February 2021, we entered into an amendment to the Sutro Biopharma Supply Agreement and extended the term to July 31, 2022. 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 Sutro Biopharma Supply Agreement of $ 0 and $ 1.6 million for the three months ended March 31, 2022 and 2021, respectively. Accrued expenses payable to Sutro Biopharma were no longer considered as related party transactions as of March 31, 2022 and December 31, 2021 , respectively.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2022
Disclosure Text Block [Abstract]
Subsequent Event	14. Subsequent Events Subsequent to March 31, 2022, through May 6, 2022, we sold a total of 1,793,410 shares of our common stock under the ATM Sales Agreement at an average price of $ 24.95 per share, generating aggregate gross proceeds of $ 44.7 million ($ 43.6 million net of commissions and offering expenses).

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2022
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, or 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 March 31, 2022, the condensed statements of operations, comprehensive loss and stockholders’ equity for the three months ended March 31, 2022 and 2021 and the condensed statements of cash flows for the three months ended March 31, 2022 and 2021 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 months ended March 31, 2022 and 2021 are also unaudited. The results of operations for the three months ended March 31, 2022 are not necessarily indicative of the results to be expected for the year ending December 31, 2022 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, 2021 included in our Annual Report on Form 10-K filed with the SEC on February 28, 2022.
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, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash We consider all highly liquid investments purchased with original maturities of three months or less from the date of purchase to be cash and cash equivalents. Cash equivalents consist primarily of amounts invested in money market accounts and commercial paper and are stated at their fair values. Restricted cash consists of a standby letter of credit, which was issued in the first quarter of 2021, that serves as collateral for the lease agreement for our new corporate headquarters. Cash, cash equivalents and restricted cash as reported within the condensed balance sheets that total to the same amounts shown in the condensed statement of cash flows as follows: March 31, December 31, 2022 2021 (in thousands) Cash and cash equivalents $ 201,741 $ 68,985 Restricted cash 871 871 Cash, cash equivalents and restricted cash $ 202,612 $ 69,856
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 loss. The cost of investment securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion are included in other income (expense), net. Realized gains and losses and declines in fair value judged to be other-than-temporary, if any, are also included in other income (expense), net. We evaluate securities for other-than-temporary impairment at the balance sheet date. Declines in fair value determined to be other-than-temporary are included in other income (expense), net. We classify our investments as short or long term primarily based on the remaining contractual maturity of the securities.
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, including pre-funded warrants issued, during the period, without consideration for common stock equivalents. Shares of common stock into which the pre-funded warrants may be exercised are considered outstanding for the purposes of computing net loss per share because the shares may be issued for little consideration, are fully vested and are exercisable after the original issuance date. 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 March 31, 2022 and December 31, 2021 , we recorded deferred offering costs of $ 0.5 million and $ 0.5 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) and its associated amendments (“ASC 842”), we determine if an arrangement is a lease at inception. In addition, we determine whether a lease meets the classification criteria of a finance or operating lease at the lease commencement date considering whether: (i) the lease transfers ownership of the underlying asset to the lessee at the end of the lease term; (ii) the lease grants the lessee an option to purchase the underlying asset that the lessee is reasonably certain to exercise; (iii) the lease term is for a major part of the remaining economic life of the underlying asset; (iv) the present value of the sum of the lease payments and residual value guaranteed by the lessee equals or exceeds substantially all of the fair value of the underlying asset; and (v) the underlying asset is such a specialized nature that it is expected to have no alternative use to the lessor at the end of the lease term. As of March 31, 2022 , our lease population consisted of real estate operating leases. As of March 31, 2022, we did no t have finance leases. Operating leases are included in Operating lease right-of-use ("ROU") assets, Operating lease liabilities — current and Operating lease liabilities — long term in our condensed balance sheet. ROU assets represent our right to use the underlying assets for the lease term and lease liabilities represent our obligation to make lease payments arising from the leases. Operating lease ROU assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the present value of lease payments, if the rate implicit in the lease is not readily determinable, we use our incremental borrowing rate based on the information available at the lease commencement date. We determine the incremental borrowing rate based on an analysis of corporate bond yields with a credit rating similar to us. The determination of our incremental borrowing rate requires management judgment, including development of a synthetic credit rating and cost of debt, as we currently do not carry any debt. We believe that the estimates used in determining the incremental borrowing rate are reasonable based upon current facts and circumstances. Applying different judgment to the same facts and circumstances could yield a different incremental borrowing rate. The operating lease ROU assets also include adjustments for prepayments and accrued lease payments and exclude lease incentives. ROU assets and lease liabilities may include options to extend or terminate leases if it is reasonably certain that we will exercise such options. Lease payments which are fixed and determinable are amortized as rent and lease expense on a straight-line basis over the expected lease term. Variable lease costs, which are dependent on usage, a rate or index, including common area maintenance charges, are expensed as incurred. Lease agreements that include lease and non-lease components are accounted for as a single lease component. Lease agreements with non-cancelable terms of less than 12 months are not recorded on our condensed balance sheets.
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	ecently Adopted Accounting Pronouncements In November 2021, the FASB issued ASU 2021-10, Government Assistance (Topic 832): Disclosure by Business Entities about Government Assistance , which requires disclosures about transactions with a government entity that are accounted for by applying a grant or contribution accounting model by analogy to other accounting guidance, such as a grant model within International Accounting Standard 20, Accounting for Government Grants and Disclosure of Government Assistance (Subtopic 958-605), Not-For-Profit Entities - Revenue Recognition . The required disclosures include (i) the nature of the transaction and the related accounting policy used to account for the transaction, (ii) the financial statement line items that are affected by the transactions and (iii) the significant terms and conditions of the transactions, including commitments and contingencies. This standard is effective for annual periods beginning after December 15, 2021, with early adoption and retrospective or prospective application permitted. This standard is effective for us on January 1, 2022 and only impacts annual financial statement footnote disclosures. In Note 10, "Funding Arrangement," we included disclosures on our cost-reimbursement research award from Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator ("CARB-X"). The adoption of this standard did not have a material impact on our financial statements. Recently Issued Accounting Pronouncements – Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments and has subsequently issued related amendments, collectively referred to as “Topic 326.” Topic 326 requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 is effective for fiscal years beginning after December 15, 2022 and interim periods within those fiscal years. Early adoption is permitted. We are currently assessing the impact of this standard to our financial statements and related disclosures.

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Schedule of Cash, Cash Equivalents And Restricted Cash	Cash, cash equivalents and restricted cash as reported within the condensed balance sheets that total to the same amounts shown in the condensed statement of cash flows as follows: March 31, December 31, 2022 2021 (in thousands) Cash and cash equivalents $ 201,741 $ 68,985 Restricted cash 871 871 Cash, cash equivalents and restricted cash $ 202,612 $ 69,856

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2022
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 March 31, 2022 and December 31, 2021: March 31, 2022 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 140,164 $ — $ — $ 140,164 Money market funds Level 1 23,104 — — 23,104 U.S. Treasury securities Level 1 3,000 3,000 Commercial paper Level 2 35,476 — ( 3 ) 35,473 Total cash and cash equivalents 201,744 — ( 3 ) 201,741 Investments: U.S. Treasury securities Level 1 45,191 — ( 266 ) 44,925 Commercial paper Level 2 42,940 — ( 46 ) 42,894 Corporate debt Level 2 24,779 — ( 271 ) 24,508 Asset-backed securities Level 2 13,840 — ( 62 ) 13,778 U.S. government agency securities Level 2 24,677 — ( 185 ) 24,492 Total investments 151,427 — ( 830 ) 150,597 Total assets measured at fair value $ 353,171 $ — $ ( 833 ) $ 352,338 December 31, 2021 Fair Value Amortized Gross Gross Fair Assets (in thousands) Cash and cash equivalents: Cash Level 1 $ 27,834 $ — $ — $ 27,834 Money market funds Level 1 17,555 — — 17,555 Commercial paper Level 2 23,597 — ( 1 ) 23,596 Total cash and cash equivalents 68,986 — ( 1 ) 68,985 Investments: U.S. Treasury securities Level 1 45,290 — ( 73 ) 45,217 Commercial paper Level 2 61,941 — ( 22 ) 61,919 Corporate debt Level 2 58,498 — ( 74 ) 58,424 Asset-backed securities Level 2 13,899 — ( 25 ) 13,874 U.S. government agency securities Level 2 24,714 — ( 46 ) 24,668 Total investments 204,342 — ( 240 ) 204,102 Total assets measured at fair value $ 273,328 $ — $ ( 241 ) $ 273,087
Schedule of Contractual Maturities of Investments	The following table presents the contractual maturities of our investments as of March 31, 2022 (in thousands): March 31, 2022 Fair Value Due in less than one year $ 132,900 Due in one to five years 17,697 Total $ 150,597

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	3 Months Ended
	Mar. 31, 2022
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net as of March 31, 2022 and December 31, 2021 consisted of the following: March 31, December 31, 2022 2021 (in thousands) Furniture and equipment $ 1,608 $ 1,619 Computers and computer software 439 430 Lab equipment 10,883 9,453 Leasehold improvements 1,329 — Total property and equipment 14,259 11,502 Less: accumulated depreciation and amortization ( 4,121 ) ( 3,548 ) Property and equipment, net $ 10,138 $ 7,954
Schedule of Accrued Expenses	Accrued expenses as of March 31, 2022 and December 31, 2021 consisted of the following: March 31, December 31, 2022 2021 (in thousands) Preclinical studies $ 5,327 $ 5,039 Clinical studies 475 — Professional fees 972 400 Other accrued expenses 970 3,348 Total $ 7,744 $ 8,787

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2022
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): March 31, 2022 Cash paid for operating lease liabilities $ 621 Operating lease right-of-use assets 26,121 Current operating lease liabilities $ 6,578 Non-current operating lease liabilities 15,832 Total lease liabilities $ 22,410 Weighted-average remaining lease term (in years) 3.54 Weighted-average discount rate 7.6 %
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities as of March 31, 2022 were as follows: Years ending December 31, (in thousands) Remainder of 2022 $ 5,132 2023 6,639 2024 6,805 2025 6,977 Thereafter — Total future undiscounted lease payments 25,553 Less: Imputed interest ( 3,143 ) Total lease liabilities $ 22,410 Future minimum payments required under operating leases as of December 31, 2021 were as follows: Years ending December 31, (in thousands) 2022 (1) $ ( 105 ) 2023 6,639 2024 6,805 2025 6,976 Thereafter — Total future undiscounted lease payments 20,315 Less: Imputed interest ( 3,532 ) Total lease liabilities $ 16,783 (1) Maturities for 2022 are net of lease incentives of $ 0.9 million allocated to the Palo Alto office.

Common Stock (Tables)

Common Stock (Tables)	3 Months Ended
	Mar. 31, 2022
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: March 31, December 31, 2022 2021 Options issued and outstanding 6,797,419 5,295,007 Restricted stock units outstanding 373,441 — Shares available for future stock option grants 6,789,842 6,104,756 Total 13,960,702 11,399,763

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	3 Months Ended
	Mar. 31, 2022
Nonvested Restricted Stock Shares Activity	RSU activity for the three months ended March 31, 2022 was as follows: Shares Weighted- Unvested at December 31, 2021 — $ — Granted 373,823 24.67 Vested — — Cancelled ( 382 ) 24.79 Unvested at March 31, 2022 373,441 24.67
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 months ended March 31, 2022 and 2021 using the following weighted-average assumptions: Three Months Ended March 31, 2022 2021 Fair Value Assumptions Expected volatility 78.1 % - 78.9 % 81.0 % - 82.5 % Expected dividend yield 0 % 0 % Expected term (in years) 5.4 5.5 Risk-free interest rate 1.6 % - 2.4 % 0.5 % - 1.0 %
2020 Plan and 2014 Plan
Summary of Activity Under Stock Option Plans	ctivity under our 2020 Plan and 2014 Plan, which excludes options to purchase 62,382 shares granted outside of the 2020 Plan and 2014 Plan, was as follows: Options Outstanding Stock Option Activity Options Number Weighted- Weighted- Aggregate Balances — December 31, 2021 6,104,756 5,295,007 $ 9.30 Additional shares authorized 2,651,598 — Options granted ( 1,605,819 ) 1,605,819 $ 24.57 Options exercised — ( 91,044 ) $ 3.18 Options forfeited 12,363 ( 12,363 ) $ 22.16 Balances — March 31, 2022 7,162,898 6,797,419 $ 12.96 8.08 $ 78,759 Vested and expected to vest — March 31, 2022 6,797,419 $ 12.96 8.08 $ 78,759 Exercisable at March 31, 2022 2,828,303 $ 5.35 6.90 $ 53,676
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 months ended March 31, 2022 and 2021 using the following weighted-average assumptions: Three Months Ended March 31, 2022 2021 Fair Value Assumptions Expected volatility 86.7 % - 97.5 % 105.8 % - 158.2 % Expected dividend yield 0 % 0 % Expected term (in years) 0.5 - 2.0 0.4 - 2.0 Risk-free interest rate 0.1 % - 0.5 % 0.1 % - 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 months ended March 31, 2022 and 2021 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 March 31, 2022 2021 (in thousands) Research and development $ 1,775 $ 683 General and administrative 2,324 1,182 Total $ 4,099 $ 1,865

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2022
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 2022 2021 Net loss (in thousands) $ ( 38,986 ) $ ( 21,220 ) Weighted-average shares outstanding used in computing net (1) 57,547,808 51,174,978 Net loss per share, basic and diluted $ ( 0.68 ) $ ( 0.41 ) (1) Includes shares of common stock into which pre-funded warrants may be exercised. See Note 8 - Pre-Funded Warrants.
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 months ended March 31, 2022 and 2021 because including them would have been antidilutive: As of March 31, 2022 2021 Stock options 6,859,801 4,863,399 Restricted stock units 373,441 — Total 7,233,242 4,863,399

Company Organization and Natu_2

Company Organization and Nature of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Feb. 28, 2022	Jan. 31, 2022	Mar. 31, 2022
Over-Allotment Option [Member]
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Shares issued		2,500,000
Common stock price per share		$ 20
Pre-funded warrants to purchase shares		2,500,000
Prefunded Warrants Price Per Share		$ 19.999
Underwriters' option to purchase additional share	750,000
Net proceeds from follow on offering	$ 107.6
Pneumococcal Conjugate Vaccine
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Global target revenue			$ 7,000

Basis of Presentation and Sum_4

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2022USD ($)Lease	Dec. 31, 2021USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Number of finance lease | Lease	0
ROU assets	$ 26,121	$ 27,958
Operating lease liabilities	22,410	16,783
Other Assets
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred offering costs	$ 500	$ 500

Basis of Presentation and Sum_5

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Cash, Cash Equivalents And Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 201,741	$ 68,985
Restricted Cash	871	871
Cash, cash equivalents and restricted cash	$ 202,612	$ 69,856	$ 199,810	$ 386,200

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2022USD ($)Security	Dec. 31, 2021USD ($)Security
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Fair value liabilities transferred from level 1 to level 2	$ 0	$ 0
Fair value assets transferred into level 3	0	0
Fair value assets transferred out of level 3	0	0
Fair value liabilities transferred into level 3	0	0
Fair value liabilities transferred out of level 3	$ 0	$ 0
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Number of securities | Security	0	0

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets:
Investments, Fair Value	$ 150,597
Fair Value, Recurring
Assets:
Cash and cash equivalents, Amortized Cost	201,744	$ 68,986
Cash and cash equivalents, Gross Unrealized Losses	(3)	(1)
Cash and cash equivalents, Fair Value	201,741	68,985
Investments, Amortized Cost	151,427	204,342
Investments, Gross Unrealized Losses	(830)	(240)
Investments, Fair Value	150,597	204,102
Total assets measured at fair value, Amortized Cost	353,171	273,328
Total assets measured at fair value, Gross Unrealized Losses	833	241
Total assets measured at fair value, Fair Value	352,338	273,087
Fair Value, Recurring | Cash | Level 1
Assets:
Cash and cash equivalents, Amortized Cost	140,164	27,834
Cash and cash equivalents, Fair Value	140,164	27,834
Fair Value, Recurring | Money Market Funds | Level 1
Assets:
Cash and cash equivalents, Amortized Cost	23,104	17,555
Cash and cash equivalents, Fair Value	23,104	17,555
Fair Value, Recurring | U.S. Treasury Securities | Level 1
Assets:
Cash and cash equivalents, Amortized Cost	3,000
Cash and cash equivalents, Fair Value	3,000
Investments, Amortized Cost	45,191	45,290
Investments, Gross Unrealized Losses	(266)	(73)
Investments, Fair Value	44,925	45,217
Fair Value, Recurring | Commercial Paper | Level 2
Assets:
Cash and cash equivalents, Amortized Cost	35,476	23,597
Cash and cash equivalents, Gross Unrealized Losses	(3)	(1)
Cash and cash equivalents, Fair Value	35,473	23,596
Investments, Amortized Cost	42,940	61,941
Investments, Gross Unrealized Losses	(46)	(22)
Investments, Fair Value	42,894	61,919
Fair Value, Recurring | U.S. Government Agency Securities | Level 2
Assets:
Investments, Amortized Cost	24,677	24,714
Investments, Gross Unrealized Losses	(185)	(46)
Investments, Fair Value	24,492	24,668
Fair Value, Recurring | Corporate Debt | Level 2
Assets:
Investments, Amortized Cost	24,779	58,498
Investments, Gross Unrealized Losses	(271)	(74)
Investments, Fair Value	24,508	58,424
Fair Value, Recurring | Asset-backed Securities | Level 2
Assets:
Investments, Amortized Cost	13,840	13,899
Investments, Gross Unrealized Losses	(62)	(25)
Investments, Fair Value	$ 13,778	$ 13,874

Fair Value Measurements and F_5

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Contractual Maturities of Investments (Details) $ in Thousands	Mar. 31, 2022USD ($)
Fair Value Disclosures [Abstract]
Due in less than one year	$ 132,900
Due in one to five years	17,697
Total	$ 150,597

Balance Sheet Details - Schedul

Balance Sheet Details - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Total property and equipment	$ 14,259	$ 11,502
Less: accumulated depreciation and amortization	(4,121)	(3,548)
Property and equipment, net	10,138	7,954
Furniture and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	1,608	1,619
Computers and Computer Software
Property Plant And Equipment [Line Items]
Total property and equipment	439	430
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	10,883	9,453
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,329	$ 0

Balance Sheet Details - Additio

Balance Sheet Details - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 0.6	$ 0.3

Balance Sheet Details - Sched_2

Balance Sheet Details - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Accrued Liabilities Current [Abstract]
Preclinical studies	$ 5,327	$ 5,039
Clinical Studies	475	0
Professional fees	972	400
Other accrued expenses	970	3,348
Total	$ 7,744	$ 8,787

Leases - Additional Information

Leases - Additional Information (Details) $ in Millions	1 Months Ended					3 Months Ended
	Feb. 28, 2022	Jan. 31, 2021RenewalOption	Nov. 30, 2020	Jul. 31, 2019	Jul. 31, 2016RenewalOption	Mar. 31, 2022USD ($)	Mar. 31, 2021USD ($)
Lessee Lease Description [Line Items]
Operating leases, rent expense recognized | $						$ 2.2	$ 0.4
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					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
Lease Termination Date	Feb. 12, 2022
New Corporate Headquarters Facility
Lessee Lease Description [Line Items]
Lease expiration date		Dec. 31, 2025
Operating lease, renewal term		60 months
Operating lease, extended term		60 days
Number of renewal options		2
Palo Alto
Lessee Lease Description [Line Items]
Operating lease, extended maturity date		Mar. 3, 2022

Leases - Schedule of Informatio

Leases - Schedule of Information Related to ROU Assets and Lease Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Cash paid for operating lease liabilities	$ 621
Operating lease right-of-use assets	26,121	$ 27,958
Current operating lease liabilities	6,578	5,276
Non-current operating lease liabilities	15,832	11,507
Total lease liabilities	$ 22,410	$ 16,783
Weighted-average remaining lease term (in years)	3 years 6 months 14 days
Weighted-average discount rate	7.60%

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Remainder of 2022	$ 5,132	$ (105)	[1]
2023	6,639	6,639
2024	6,805	6,805
2025	6,977	6,976
Total future undiscounted lease payments	25,553	20,315
Less: Imputed interest	(3,143)	(3,532)
Total lease liabilities	$ 22,410	$ 16,783
[1]	Maturities for 2022 are net of lease incentives of $ 0.9 million allocated to the Palo Alto office.

Leases - Schedule of Maturiti_2

Leases - Schedule of Maturities of Lease Liabilities (Parenthetical) (Details) $ in Millions	Mar. 31, 2022USD ($)
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
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
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

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	12 Months Ended
	Feb. 28, 2022	Jan. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	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			56,499,544	53,031,978
Common stock, shares outstanding			56,499,544	53,031,978
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			$ 3,115
Equity incentive plan, shares issued			62,382
Over-Allotment Option
Class Of Stock [Line Items]
Shares issued		2,500,000
Common stock price per share		$ 20
Pre-funded warrants to purchase shares		2,500,000
Prefunded Warrants Price Per Share		$ 19.999
Underwriters' option to purchase additional share	750,000
Net proceeds from follow on offering	$ 107,600
ATM Sales Agreement | Jefferies LLC
Class Of Stock [Line Items]
Maximum commission percentage of gross proceeds from common stock sold					3.00%
Issuance of common stock in connection follow-on public offering, net of issuance costs, shares			693,567
Average price			$ 25.29
Aggregate gross proceeds from issuance of common stock			$ 17,500
Proceeds from issuance of stock, net of commission and offering expenses			$ 17,000
ATM Sales Agreement | Maximum | Jefferies LLC
Class Of Stock [Line Items]
Aggregate offering price					$ 150,000

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Stock Shares Reserved for Future Issuance (Details) - 2020 Plan and 2014 Plan - shares	Mar. 31, 2022	Dec. 31, 2021
Class Of Stock [Line Items]
Common stock reserved for future issuances	13,960,702	11,399,763
Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuances	6,797,419	5,295,007
Restricted stock units outstanding
Class Of Stock [Line Items]
Common stock reserved for future issuances	373,441
Shares Available for Future Stock Option Grants
Class Of Stock [Line Items]
Common stock reserved for future issuances	6,789,842	6,104,756

Pre-Funded Warrants - Additiona

Pre-Funded Warrants - Additional Information (Details) - $ / shares	1 Months Ended
	Jan. 31, 2022	Mar. 31, 2022
Class Of Stock [Line Items]
Warrant exercised	0.001	0
Pre-funded warrants of common stock shares outstanding Immediately after effect to the exercise	9.99%
Combined voting power of securities outstanding immediately after effect to the exercise	9.99%
Increase or Decrease of Pre-funded Warrant Percentage Not Exceed	19.99%
Over-Allotment Option
Class Of Stock [Line Items]
Shares issued	2,500,000
Common stock price per share	$ 20
Pre-funded warrants to purchase shares	2,500,000
Prefunded Warrants Price Per Share	$ 19.999
Pre-funded warrant recorded as a component of stockholders' equity within additional paid-in-capital	$ 0.001

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 01, 2021	Jun. 11, 2020	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
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			6,484		7,410
Options granted			62,382
Exercise of stock options (in shares)			91,044	267,208
Weighted-average price per share			$ 3.18	$ 1.82
Weighted-average grant date fair value of options granted			$ 16.34	$ 17.70
Intrinsic value of the stock options exercised			$ 1.8	$ 6.4
Restricted stock units outstanding
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
Vesting percentage for stock options granted, Six months thereafter		12.50%
Other Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period for stock options granted		3 years 6 months
Vesting percentage for stock options granted, Six months thereafter		12.50%
Weighted-average grant date fair value of options granted			$ 24.67
Closing price of common stock			$ 24.15
Unrecognized stock-based compensation cost			$ 7
Unrecognized cost expected to be recognized over a weighted-average period (in years)			3 years 6 months
Number of restricted stock units vested			0
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
Percentage of outstanding number of shares		5.00%
Available for issuance of shares increased	2,651,598
Aggregate number of shares available for issuance			7,162,898
Number of shares outstanding			3,228,500
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding			3,568,919
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	530,319
Aggregate number of shares available for issuance			1,601,023
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
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
	Mar. 31, 2022	Mar. 31, 2021
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	$ 3.18	$ 1.82
2020 Plan and 2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Available for Grant, Beginning Balance	6,104,756
Options Available for Grant, Additional shares authorized	2,651,598
Options Available for Grant, granted	(1,605,819)
Options Available for Grant, forfeited	12,363
Options Available for Grant, Ending Balance	7,162,898
Number of Options, Beginning Balance	5,295,007
Number of Options, granted	1,605,819
Number of Options, exercised	(91,044)
Number of Options, forfeited	(12,363)
Number of Options, Ending Balance	6,797,419
Number of Options, Vested and expected to vest	6,797,419
Number of Options, Exercisable	2,828,303
Weighted-Average Exercise Price Per Share, Beginning Balance	$ 9.30
Weighted-Average Exercise Price Per Share, Options granted	24.57
Weighted-Average Exercise Price Per Share, Options exercised	3.18
Weighted-Average Exercise Price Per Share, Options forfeited	22.16
Weighted-Average Exercise Price Per Share, Ending Balance	12.96
Weighted-Average Exercise Price Per Share, Vested and expected to vest	12.96
Weighted-Average Exercise Price Per Share, Exercisable	$ 5.35
Weighted-Average Remaining Contractual Term (Years)	8 years 29 days
Weighted-Average Remaining Contractual Term (Years), Vested and expected to vest	8 years 29 days
Weighted-Average Remaining Contractual Term (Years), Exercisable	6 years 10 months 24 days
Aggregate Intrinsic Value	$ 78,759
Aggregate Intrinsic Value, Vested and expected to vest	78,759
Aggregate Intrinsic Value, Exercisable	$ 53,676

Equity Incentive Plan - Nonvest

Equity Incentive Plan - Nonvested Restricted Stock Shares Activity (Details)	3 Months Ended
	Mar. 31, 2022USD ($)shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted | shares	373,823
Cancelled | shares	(382)
Unvested at March 31. 2022 | shares	373,441
Weighted average grant date fair value, granted | $	$ 24,670
Weighted average grant date fair value, cancelled | $	24,790
Weighted average grant date fair value | $	$ 24,670

Equity Incentive Plans - Summ_2

Equity Incentive Plans - Summary of Estimated Fair Value of Employee Stock Options (Details)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Fair Value Assumptions
Expected volatility, Minimum	78.10%	81.00%
Expected volatility, Maximum	78.90%	82.50%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	5 years 4 months 24 days	5 years 6 months
Risk-free interest rate, Minimum	1.60%	0.50%
Risk-free interest rate, Maximum	2.40%	1.00%

Equity Incentive Plans - Summ_3

Equity Incentive Plans - Summary of Estimated Fair Value of Shares Under Employee Stock Purchase Plan (Details)	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Fair Value Assumptions
Expected volatility, Minimum	78.10%	81.00%
Expected volatility, Maximum	78.90%	82.50%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	5 years 4 months 24 days	5 years 6 months
Risk-free interest rate, Minimum	1.60%	0.50%
Risk-free interest rate, Maximum	2.40%	1.00%
2020 Employee Stock Purchase Plan
Fair Value Assumptions
Expected volatility, Minimum	86.70%	105.80%
Expected volatility, Maximum	97.50%	158.20%
Expected dividend yield	0.00%	0.00%
Risk-free interest rate, Minimum	0.10%	0.10%
Risk-free interest rate, Maximum	0.50%	0.20%
2020 Employee Stock Purchase Plan | Minimum
Fair Value Assumptions
Expected term (in years)	6 months	4 months 24 days
2020 Employee Stock Purchase Plan | Maximum
Fair Value Assumptions
Expected term (in years)	2 years	2 years

Equity Incentive Plans - Summ_4

Equity Incentive Plans - Summary of Stock-based Compensation Expense (Details) - 2014 Plan, 2020 Plan and 2020 ESPP - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 4,099	$ 1,865
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	1,775	683
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,324	$ 1,182

Funding Arrangement - Additiona

Funding Arrangement - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Apr. 30, 2021	Jul. 31, 2019	Mar. 31, 2022	Mar. 31, 2021	Jan. 31, 2022	Dec. 31, 2021	Aug. 04, 2021	Jul. 31, 2020
Funding Arrangement [Line Items]
Grant income			$ 160
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
Grant income			200	$ 0
Cost Reimbursement Sub-Award Agreement | Maximum
Funding Arrangement [Line Items]
Initial funding committed by award		$ 1,600
Total funding committed by award, available upon achievement of development milestones		$ 15,100
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
Potential funding committed by award					$ 13,900
Grant receivable on unreimbursed, eligible costs incurred			$ 100			$ 1,200
CARB-X Agreement | Maximum
Funding Arrangement [Line Items]
Initial funding committed by award								$ 2,700
Additional funding committed by award							3,200
Potential funding committed by award							$ 29,700
CARB-X Agreement | Minimum
Funding Arrangement [Line Items]
Initial funding committed by award								$ 1,600

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
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net loss (in thousands)	$ (38,986)	$ (21,220)
Weighted-average shares outstanding used in computing net loss per share, basic and diluted	57,547,808	51,174,978
Net loss per share, basic and diluted	$ (0.68)	$ (0.41)

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
	Mar. 31, 2022	Mar. 31, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	7,233,242	4,863,399
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	373,441
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	6,859,801	4,863,399

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	3 Months Ended
	Mar. 31, 2022USD ($)
Income Tax Disclosure [Abstract]
Tax provision	$ 0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	May 29, 2018	Mar. 31, 2022	Mar. 31, 2021	Jan. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Common stock, shares owned		56,499,544			53,031,978
Pre -funded Warrant exercised		0		0.001
Sutro Biopharma, Inc | License Agreement
Related Party Transaction [Line Items]
Percentage of royalty payment on annual net sales of vaccine products for human health		4.00%
Percentage of royalty payment on net sales of vaccine compositions for animal health		2.00%
Sutro Biopharma, Inc | Supply Agreement
Related Party Transaction [Line Items]
Expenses related to agreement		$ 0	$ 1,600,000
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

Subsequent Events Additional In

Subsequent Events Additional Information (Details) - ATM Sales Agreement - Subsequent Event $ / shares in Units, $ in Millions	1 Months Ended
	May 06, 2022USD ($)$ / sharesshares
Subsequent Event [Line Items]
Issuance of common stock in connection follow-on public offering, net of issuance costs, shares | shares	1,793,410
Average price | $ / shares	$ 24.95
Aggregate gross proceeds from issuance of common stock	$ 44.7
Proceeds from issuance of stock, net of commission and offering expenses	$ 43.6