Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted in accordance with such rules and regulations. Certain changes in presentation were made in the condensed balance sheet as of December 31, 2019 to conform to the presentation of the condensed balance sheet as of September 30, 2020.
Unaudited Interim Condensed Financial Statements	Unaudited Interim Condensed Financial Statements The condensed balance sheet as of September 30, 2020, the condensed statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2020 and 2019, and the condensed statements of cash flows for the nine months ended September 30, 2020 and 2019, are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of our financial information. The financial data disclosed in the footnotes to the condensed financial statements related to the three and nine months ended September 30, 2020 and 2019 are also unaudited. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other future annual or interim period. These interim condensed financial statements should be read in conjunction with our audited annual financial statements included in the prospectus dated June 11, 2020 that forms a part of our Registration Statements on Form S-1 (File Nos. 333-238630 and 333-239110) as filed with the SEC pursuant to Rule 424(b)(4) and Rule 462(b) promulgated under the Securities Act of 1933, as amended.
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 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.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs consist of fees and expenses incurred in connection with the sale of our common stock in the IPO, including legal, accounting, printing and other IPO-related costs. Prior to the completion of our IPO, deferred offering costs were included in Other assets on the condensed balance sheet. In connection with and as of the closing of our IPO, these costs were reclassified to Additional paid-in capital, representing a reduction to the IPO proceeds. As of September 30, 2020, $3.4 million of these IPO-related costs are included in the Additional paid-in capital line item on the condensed balance sheet. As of December 31, 2019, $1.1 million of deferred offering costs were included in Other assets on the balance sheet.
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. We currently invest in money market funds. 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 cash equivalents. We have not experienced any losses on our deposits of cash and cash equivalents. 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 Issued Accounting Pronouncements Adopted And Not Yet Adopted	Recently Adopted Accounting Pronouncements In June 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting for share-based payments granted to non-employees for goods and services. This standard expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods and services. Consequently, the accounting for share-based payments to non-employees and employees was substantially aligned. The ASU supersedes Subtopic 505-50, Equity—Equity-Based Payments to Non-Employees. This standard is effective for fiscal years beginning after December 15, 2019 and interim periods within fiscal years beginning after December 15, 2020. The standard should be adopted on a modified retrospective basis which recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We adopted this ASU as of January 1, 2020. The adoption of this ASU had no material impact on our financial statements or disclosures. Recently Issued Accounting Pronouncements—Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 was subsequently amended by ASU 2018-01, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2019-10 and ASU 2020-05, which the FASB issued in January 2018, July 2018, July 2018, December 2018, March 2019, November 2019 and June 2020, respectively (collectively, the “amended ASU 2016-02”). The amended ASU 2016-02 requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new standard establishes a right-of-use (“ROU”) model that requires a lessee to recognize a ROU asset and a lease liability on the balance sheet for all leases with a term longer than 12 months. Under the new standard, leases will be classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement. The new standard is effective for us on January 1, 2022, with early adoption permitted. We expect to adopt the new standard on the effective date. The new standard requires an entity to adopt using one of two approaches, either (i) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (ii) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. Although we are currently evaluating the impact of adoption on our financial statements and related disclosures, we believe the most significant changes will be the recognition of the ROU assets and the related lease liabilities for our operating leases on our condensed balance sheets. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740). The amendments in ASU 2019-12 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify U.S. GAAP or other areas of Topic 740 by clarifying and amending existing guidance. The new standard is effective for us on January 1, 2022 and for interim periods beginning on January 1, 2023. We are currently evaluating the impact that the standard will have on our condensed financial statements and related disclosures.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted in accordance with such rules and regulations. Certain changes in presentation were made in the condensed balance sheet as of December 31, 2019 to conform to the presentation of the condensed balance sheet as of September 30, 2020.

Unaudited Interim Condensed Financial Statements

The condensed balance sheet as of September 30, 2020, the condensed statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2020 and 2019, and the condensed statements of cash flows for the nine months ended September 30, 2020 and 2019, are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of our financial information. The financial data disclosed in the footnotes to the condensed financial statements related to the three and nine months ended September 30, 2020 and 2019 are also unaudited. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other future annual or interim period. These interim condensed financial statements should be read in conjunction with our audited annual financial statements included in the prospectus dated June 11, 2020 that forms a part of our Registration Statements on Form S-1 (File Nos. 333-238630 and 333-239110) as filed with the SEC pursuant to Rule 424(b)(4) and Rule 462(b) promulgated under the Securities Act of 1933, as amended.

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 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.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.

Deferred Offering Costs

Deferred offering costs consist of fees and expenses incurred in connection with the sale of our common stock in the IPO, including legal, accounting, printing and other IPO-related costs. Prior to the completion of our IPO, deferred offering costs were included in Other assets on the condensed balance sheet. In connection with and as of the closing of our IPO, these costs were reclassified to Additional paid-in capital, representing a reduction to the IPO proceeds. As of September 30, 2020, $3.4 million of these IPO-related costs are included in the Additional paid-in capital line item on the condensed balance sheet. As of December 31, 2019, $1.1 million of deferred offering costs were included in Other assets on the balance sheet.

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. We currently invest in money market funds. 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 cash equivalents. We have not experienced any losses on our deposits of cash and cash equivalents.

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 Issued Accounting Pronouncements Adopted And Not Yet Adopted

Recently Adopted Accounting Pronouncements

In June 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting for share-based payments granted to non-employees for goods and services. This standard expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods and services. Consequently, the accounting for share-based payments to non-employees and employees was substantially aligned. The ASU supersedes Subtopic 505-50, Equity—Equity-Based Payments to Non-Employees. This standard is effective for fiscal years beginning after December 15, 2019 and interim periods within fiscal years beginning after December 15, 2020. The standard should be adopted on a modified retrospective basis which recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We adopted this ASU as of January 1, 2020. The adoption of this ASU had no material impact on our financial statements or disclosures.

Recently Issued Accounting Pronouncements—Not Yet Adopted

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 was subsequently amended by ASU 2018-01, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2019-10 and ASU 2020-05, which the FASB issued in January 2018, July 2018, July 2018, December 2018, March 2019, November 2019 and June 2020, respectively (collectively, the “amended ASU 2016-02”). The amended ASU 2016-02 requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new standard establishes a right-of-use (“ROU”) model that requires a lessee to recognize a ROU asset and a lease liability on the balance sheet for all leases with a term longer than 12 months. Under the new standard, leases will be classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement.

The new standard is effective for us on January 1, 2022, with early adoption permitted. We expect to adopt the new standard on the effective date. The new standard requires an entity to adopt using one of two approaches, either (i) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (ii) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. Although we are currently evaluating the impact of adoption on our financial statements and related disclosures, we believe the most significant changes will be the recognition of the ROU assets and the related lease liabilities for our operating leases on our condensed balance sheets.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740). The amendments in ASU 2019-12 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify U.S. GAAP or other areas of Topic 740 by clarifying and amending existing guidance. The new standard is effective for us on January 1, 2022 and for interim periods beginning on January 1, 2023. We are currently evaluating the impact that the standard will have on our condensed financial statements and related disclosures.