Novavax (NVAX) 10-Q 10 Aug 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
Document and Entity Information
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Entity Registrant Name	NOVAVAX INC
Entity Central Index Key	0001000694
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Trading Symbol	NVAX
Entity Common Stock, Shares Outstanding		61,278,148
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Shell Company	false
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	000-26770
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	22-2816046
Entity Address, Address Line One	21 Firstfield Road
Entity Address, City or Town	Gaithersburg
Entity Address, Country	MD
Entity Address, Postal Zip Code	20878
City Area Code	240
Local Phone Number	268-2000
Title of 12(b) Security	Common Stock, Par Value $0.01 per share
Security Exchange Name	NASDAQ

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 424,395	$ 78,823
Marketable securities	77,902	0
Restricted cash	106,768	2,947
Accounts receivable		7,500
Prepaid expenses and other current assets	27,316	7,977
Total current assets	636,381	97,247
Restricted cash	411	410
Property and equipment, net	115,375	11,445
Intangible assets, net	5,250	5,581
Goodwill	118,849	51,154
Other non-current assets	55,961	7,120
Total assets	932,227	172,957
Current liabilities:
Accounts payable	9,242	2,910
Accrued expenses	38,690	14,867
Accrued interest	5,078	5,078
Deferred revenue	158,851	1,678
Other current liabilities	1,470	1,262
Total current liabilities	213,331	25,795
Deferred revenue	2,500	2,500
Convertible notes payable	321,323	320,611
Other non-current liabilities	10,725	10,068
Total liabilities	547,879	358,974
Commitments and contingencies
Preferred stock, $0.01 par value, 2,000,000 shares authorized; 438,885 shares of redeemable Series A Convertible Preferred Stock issued and outstanding at June 30, 2020 and no shares issued and outstanding at December 31, 2019	199,822	0
Stockholders' equity (deficit):
Common stock, $0.01 par value, 600,000,000 shares authorized at June 30, 2020 and December 31, 2019; 61,262,632 shares issued and 61,211,223 shares outstanding at June 30, 2020 and 32,399,352 shares issued and 32,352,416 shares outstanding at December 31, 2019	612	324
Additional paid-in capital	1,699,072	1,260,551
Accumulated deficit	(1,499,325)	(1,431,801)
Treasury stock, 51,409 shares, cost basis at March 31, 2020 and 46,936 shares, cost basis at December 31, 2019	(2,638)	(2,583)
Accumulated other comprehensive loss	(13,195)	(12,508)
Total stockholders' equity (deficit)	184,526	(186,017)
Total liabilities, preferred stock and stockholders' equity (deficit)	$ 932,227	$ 172,957

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Preferred stock, Par or stated value per share	$ 0.01	$ 0.01
Preferred stock, Shares authorized	2,000,000	200,000
Common stock, par value per share	$ 0.01	$ 0.01
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	61,262,632	32,399,352
Common stock, shares outstanding	61,211,223	32,352,416
Treasury stock, shares	51,409	46,936
Redeemable Series A Convertible Preferred Stock
Preferred stock, Shares issued	438,885	0
Preferred stock, Shares outstanding	438,885	0

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue:
Total revenue	$ 35,538	$ 3,357	$ 38,915	$ 7,339
Expenses:
Research and development	34,846	30,417	51,741	65,890
General and administrative	17,719	9,606	27,098	18,338
Total expenses	52,565	40,023	78,839	84,228
Loss from operations	(17,027)	(36,666)	(39,924)	(76,889)
Other income (expense):
Investment income	297	474	732	894
Interest expense	(3,403)	(3,403)	(6,806)	(6,806)
Other income (expense)	2,612	(8)	2,613	(20)
Net loss	$ (17,521)	$ (39,603)	$ (43,385)	$ (82,821)
Basic and diluted net loss per share	$ (0.30)	$ (1.69)	$ (0.84)	$ (3.77)
Basic and diluted weighted average number of common shares outstanding	58,618	23,473	51,401	21,966
Grant and other [Member]
Revenue:
Total revenue	$ 35,538	$ 3,357	$ 38,915	$ 7,339

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS
Net loss	$ (17,521)	$ (39,603)	$ (43,385)	$ (82,821)
Other comprehensive income (loss):
Net unrealized gains on marketable debt securities available-for-sale	176	0	44	5
Foreign currency translation gain (loss) adjustment	1,115	70	(731)	(1,104)
Other comprehensive gain (loss)	1,291	70	(687)	(1,099)
Comprehensive loss	$ (16,230)	$ (39,533)	$ (44,072)	$ (83,920)

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss)	Total
Balance beginning at Dec. 31, 2018	$ 192,000	$ 1,144,621,000	$ (1,299,107,000)	$ (2,450,000)	$ (11,191,000)	$ (167,935,000)
Balance beginning (in shares) at Dec. 31, 2018	19,245,302
Balance ending at Mar. 31, 2019	$ 235,000	1,206,317,000	(1,342,325,000)	(2,450,000)	(12,360,000)	(150,583,000)
Balance ending (in shares) at Mar. 31, 2019	23,495,466
Balance beginning at Dec. 31, 2018	$ 192,000	1,144,621,000	(1,299,107,000)	(2,450,000)	(11,191,000)	(167,935,000)
Balance beginning (in shares) at Dec. 31, 2018	19,245,302
Non-cash compensation cost for stock options, RSUs, SARs and ESPP		10,179,000				10,179,000
Exercise of stock options/Purchases under ESPP	$ 1,000	941,000				942,000
Exercise of stock options/Purchases under ESPP, (in shares)	51,388
Fractional shares purchased in stock split				(1,000)		(1,000)
Issuance of common stock, net of issuance costs	$ 42,000	55,200,000				55,242,000
Issuance of common stock, net of issuance costs, (in shares)	4,198,776
Unrealized gain on marketable securities					5,000	5,000
Foreign currency translation adjustment					(1,104,000)	(1,104,000)
Net loss			(82,821,000)			(82,821,000)
Balance ending at Jun. 30, 2019	$ 235,000	1,210,941,000	(1,381,928,000)	(2,451,000)	(12,290,000)	(185,493,000)
Balance ending (in shares) at Jun. 30, 2019	23,495,466
Balance beginning at Mar. 31, 2019	$ 235,000	1,206,317,000	(1,342,325,000)	(2,450,000)	(12,360,000)	(150,583,000)
Balance beginning (in shares) at Mar. 31, 2019	23,495,466
Non-cash compensation cost for stock options, RSUs, SARs and ESPP	$ 0	4,621,000	0	0	0	4,621,000
Fractional shares purchased in stock split	0	0	0	(1,000)	0	(1,000)
Issuance of common stock, net of issuance costs	$ 0	3,000	0	0	0	3,000
Issuance of common stock, net of issuance costs, (in shares)	0
Foreign currency translation adjustment	$ 0	0	0	0	70,000	70,000
Net loss	0	0	(39,603,000)	0	0	(39,603,000)
Balance ending at Jun. 30, 2019	$ 235,000	1,210,941,000	(1,381,928,000)	(2,451,000)	(12,290,000)	(185,493,000)
Balance ending (in shares) at Jun. 30, 2019	23,495,466
Balance beginning at Dec. 31, 2019	$ 324,000	1,260,551,000	(1,431,801,000)	(2,583,000)	(12,508,000)	(186,017,000)
Balance beginning (in shares) at Dec. 31, 2019	32,399,352
Balance ending at Mar. 31, 2020	$ 539,000	1,450,279,000	(1,457,665,000)	(2,638,000)	(14,486,000)	(23,971,000)
Balance ending (in shares) at Mar. 31, 2020	53,906,322
Balance beginning at Dec. 31, 2019	$ 324,000	1,260,551,000	(1,431,801,000)	(2,583,000)	(12,508,000)	(186,017,000)
Balance beginning (in shares) at Dec. 31, 2019	32,399,352
Preferred stock beneficial conversion feature		24,139,000	(24,139,000)
Non-cash compensation cost for stock options, RSUs, SARs and ESPP		11,897,000				11,897,000
Exercise of stock options/Vesting of RSUs/Purchases under ESPP	$ 3,000	9,007,000		(55,000)		8,955,000
Exercise of stock options/Vesting of RSUs/Purchases under ESPP (in shares)	350,054
Issuance of common stock, net of issuance costs	$ 285,000	393,478,000				393,763,000
Issuance of common stock, net of issuance costs, (in shares)	28,513,226
Unrealized gain on marketable securities					44,000	44,000
Foreign currency translation adjustment					(731,000)	(731,000)
Net loss			(43,385,000)			(43,385,000)
Balance ending at Jun. 30, 2020	$ 612,000	1,699,072,000	(1,499,325,000)	(2,638,000)	(13,195,000)	184,526,000
Balance ending (in shares) at Jun. 30, 2020	61,262,632
Balance beginning at Mar. 31, 2020	$ 539,000	1,450,279,000	(1,457,665,000)	(2,638,000)	(14,486,000)	(23,971,000)
Balance beginning (in shares) at Mar. 31, 2020	53,906,322
Preferred stock beneficial conversion feature	$ 0	24,139,000	(24,139,000)	0	0	0
Non-cash compensation cost for stock options, RSUs, SARs and ESPP	0	7,932,000	0	0	0	7,932,000
Exercise of stock options/Vesting of RSUs/Purchases under ESPP	$ 3,000	8,947,000	0	0	0	8,950,000
Exercise of stock options/Vesting of RSUs/Purchases under ESPP (in shares)	316,815
Issuance of common stock, net of issuance costs	$ 70,000	207,775,000	0	0	0	207,845,000
Issuance of common stock, net of issuance costs, (in shares)	7,039,495
Unrealized gain on marketable securities	$ 0	0	0	0	176,000	176,000
Foreign currency translation adjustment	0	0	0	0	1,115,000	1,115,000
Net loss	0	0	(17,521,000)	0	0	(17,521,000)
Balance ending at Jun. 30, 2020	$ 612,000	$ 1,699,072,000	$ (1,499,325,000)	$ (2,638,000)	$ (13,195,000)	$ 184,526,000
Balance ending (in shares) at Jun. 30, 2020	61,262,632

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT)
Issuance of common stock, issuance costs	$ 2,647	$ 3	$ 5,145	$ 1,112

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating Activities:
Net loss	$ (43,385)	$ (82,821)
Reconciliation of net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	1,905	3,864
Loss on disposal of property and equipment	0	88
Amortization of debt issuance costs	712	712
Non-cash stock-based compensation	11,897	10,179
Other	(1,793)	1,269
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(61,079)	2,617
Accounts payable and accrued expenses	27,094	(10,952)
Deferred revenue	157,173	(5,577)
Net cash provided by (used in) operating activities	92,524	(80,621)
Investing Activities:
Capital expenditures	(3,884)	(1,281)
Acquisition of Praha Vaccines a.s., net of cash acquired	(164,204)	0
Proceeds from maturities of marketable securities	29,750	24,500
Purchases of marketable securities	(107,608)	(2,484)
Net cash provided by (used in) investing activities	(245,946)	20,735
Financing Activities:
Net proceeds from sale of preferred stock	199,822	0
Net proceeds from sales of common stock	393,763	55,242
Proceeds from the exercise of stock options and employee stock purchases	8,955	942
Net cash provided by financing activities	602,540	56,184
Effect of exchange rate on cash, cash equivalents and restricted cash	276	(22)
Net increase (decrease) in cash, cash equivalents and restricted cash	449,394	(3,724)
Cash, cash equivalents and restricted cash at beginning of period	82,180	81,959
Cash, cash equivalents and restricted cash at end of period	531,574	78,235
Supplemental disclosure of non-cash activities:
Property and equipment purchases included in accounts payable and accrued expenses	2,753	146
Supplemental disclosure of cash flow information:
Cash payments of interest	$ 6,094	$ 6,094

Organization

Organization	6 Months Ended
	Jun. 30, 2020
Organization
Organization	Note 1 – Organization Novavax, Inc. (“Novavax,” and together with its wholly owned subsidiaries, Novavax AB and Praha Vaccines a.s., the “Company”) is a late-stage biotechnology company that promotes improved global health through the discovery, development and commercialization of innovative vaccines to prevent serious infectious diseases and address urgent, global health needs. The Company’s vaccine candidates, including both its recently announced coronavirus vaccine candidate, NVX-CoV2373, as well as its other lead candidate, NanoFlu TM

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	Note 2 – Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. The consolidated balance sheet as of June 30, 2020, the consolidated statements of operations and the consolidated statements of comprehensive loss for the three and six months ended June 30, 2020 and 2019, the consolidated statements of changes in stockholders’ equity (deficit) for the three and six months ended June 30, 2020 and 2019 and the consolidated statements of cash flows for the six months ended June 30, 2020 and 2019 are unaudited, but include all adjustments (consisting of normal recurring adjustments) that the Company considers necessary for a fair presentation of the financial position, operating results, comprehensive loss, changes in stockholders’ equity (deficit) and cash flows, respectively, for the periods presented. Although the Company believes that the disclosures in these unaudited consolidated financial statements are adequate to make the information presented not misleading, certain information and footnote information normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted as permitted under the rules and regulations of the United States Securities and Exchange Commission (“SEC”). The unaudited consolidated financial statements include the accounts of Novavax, Inc. and its wholly owned subsidiaries, Novavax AB and Praha Vaccines a.s. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying unaudited consolidated financial statements are presented in U.S. dollars. The functional currency of Novavax AB, which is located in Sweden, is the local currency (Swedish Krona), and the functional currency of Praha Vaccines a.s., which is located in the Czech Republic, is the local currency (Czech Koruna). The translation of assets and liabilities of these subsidiaries to U.S. dollars is made at the exchange rate in effect at the consolidated balance sheet date, while equity accounts are translated at historical rates. The translation of the statement of operations data is made at the average exchange rate in effect for the period. The translation of operating cash flow data is made at the average exchange rate in effect for the period, and investing and financing cash flow data is translated at the exchange rate in effect at the date of the underlying transaction. Translation gains and losses are recognized as a component of accumulated other comprehensive loss in the accompanying unaudited consolidated balance sheets. The foreign currency translation adjustment balance included in accumulated other comprehensive loss was $13.2 million and $12.5 million at June 30, 2020 and December 31, 2019, respectively. The accompanying unaudited consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019. Results for this or any interim period are not necessarily indicative of results for any future interim period or for the entire year. The Company operates in one business segment. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates. Cash and Cash Equivalents Cash and cash equivalents consist of highly liquid investments with maturities of three months or less from the date of purchase. Cash and cash equivalents consist of the following at (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Cash ​ $ 124,783 ​ $ 15,863 Money market funds ​ 225,373 ​ 42,960 Asset-backed securities ​ 24,250 ​ 20,000 Treasury bills ​ 49,989 ​ — Cash and cash equivalents ​ $ 424,395 ​ $ 78,823 ​ Cash equivalents are recorded at cost, which approximate fair value due to their short-term nature. Marketable Securities Marketable securities consist of debt securities with maturities greater than three months from the date of purchase that include commercial paper, asset-backed securities, treasury bills and corporate notes. Classification of marketable securities between current and non-current is dependent upon the maturity date at the balance sheet date taking into consideration the Company's ability and intent to hold the investment to maturity. Interest and dividend income are recorded when earned and included in investment income in the consolidated statements of operations. Premiums and discounts, if any, on marketable securities are amortized or accreted to maturity and included in investment income in the consolidated statements of operations. The specific identification method is used in computing realized gains and losses on the sale of the Company's securities. The Company classifies its marketable securities with readily determinable fair values as “available-for-sale.” Investments in securities that are classified as available-for-sale are measured at fair market value in the consolidated balance sheets, and unrealized gains and losses on marketable securities are reported as a separate component of stockholders' deficit until realized. Marketable securities are evaluated periodically to determine whether a decline in value is “other-than-temporary.” The term “other-than-temporary” is not intended to indicate a permanent decline in value. Rather, it means that the prospects for a near term recovery of value are not necessarily favorable, or that there is a lack of evidence to support fair values equal to, or greater than, the carrying value of the security. Management reviews criteria, such as the magnitude and duration of the decline, as well as the Company's ability to hold the securities, including whether the Company will be required to sell a security prior to recovery of its amortized cost basis, the investment issuer's financial condition and business outlook to predict whether the loss in value is other-than-temporary. If a decline in value is determined to be other-than-temporary, the value of the security is reduced and the impairment is recorded as other income (expense) in the consolidated statements of operations. Restricted Cash The Company’s current and non-current restricted cash includes payments received under the Coalition for Epidemic Preparedness Innovations (“CEPI”) funding agreements (see Note 11), payments received under the Bill & Melinda Gates Foundation (“BMGF”) grant agreement (see Note 11), escrow funds paid in connection with the acquisition of Praha Vaccines a.s. (see Note 5) and funds received in connection with a transaction in 2019 with Catalent Maryland, Inc. (formerly Paragon Bioservices, Inc.), a unit of Catalent Biologics (“Catalent”), pursuant to which the Company agreed to sell to Catalent certain assets related to its biomanufacturing and development activities and cash collateral accounts under letters of credit that serve as security deposits for certain facility leases. The Company will utilize the CEPI and BMGF funds as it incurs expenses for services performed under these agreements. At both June 30, 2020 and December 31, 2019, the restricted cash balances (both current and non-current) consisted of $1.4 million of payments received from BMGF, $1.5 million held in escrow received in connection with the Catalent transaction and $0.4 million of security deposits. At June 30, 2020, the restricted cash balance also included $92.6 million of payments under the CEPI funding agreements and $11.2 million held in escrow that was paid by the Company in connection with the Praha Vaccines a.s. acquisition. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the statement of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Cash and cash equivalents ​ $ 424,395 ​ $ 78,823 Restricted cash current ​ 106,768 ​ 2,947 Restricted cash non-current ​ 411 ​ 410 Cash, cash equivalents and restricted cash ​ $ 531,574 ​ $ 82,180 ​ Acquisitions The Company applies the acquisition method of accounting to business combinations in accordance with ASC 805, Business Combinations. The Company’s consolidated financial statements include the operating results of an acquired entity from the date on which it obtains control of the business acquired. The Company recognizes and measures the identifiable assets acquired and liabilities assumed, as of the acquisition date, based on their estimated fair value with the excess purchase consideration, if any, recognized as goodwill. In determining fair value, the Company uses various recognized valuation methods, including the cost and market approaches. The Company initially performs these valuations based on preliminary estimates and assumptions by management or independent valuation specialists under Company supervision, where appropriate, and makes revisions as estimates and assumptions are finalized. The final determination of fair values must be completed no later than the first anniversary of the date of acquisition. The Company expenses acquisition related costs as incurred. See Note 5 for further discussion around the Company’s recent acquisition of Praha Vaccines a.s. Revenue Recognition The Company performs research and development under grant, license and clinical development agreements. Payments received in advance of work performed are recorded as deferred revenue. The Company entered into funding agreements with CEPI that provide total funding of up to $388.4 million (see Note 11). The funding includes approximately $245.9 million in the form of a grant (“CEPI Grant Funding”) and up to $142.5 million in the form of one or more forgivable no interest term loans (“CEPI Forgivable Loan Funding”). Under the CEPI Grant Funding, the Company is entitled to reimbursement for costs that support development activities of NVX-CoV2373. The CEPI Forgivable Loan Funding is designated for the prepayment of certain manufacturing activities. The funding from CEPI is critical to enable ongoing development of NVX-CoV2373, and to enable the Company to obtain product licensing to produce the vaccine for use in clinical trials and commercial distribution, if approved. The CEPI funding agreements do not provide a direct economic benefit to CEPI. Rather, the Company entered into an agreement with CEPI to attempt to develop a COVID-19 vaccine under which CEPI only benefits to the extent the arrangement furthers its public health mission. Based on these circumstances, the Company does not consider CEPI to be a customer and concluded the funding agreements are outside the scope of ASC 606, Revenue from Contracts with Customers Not-for-Profit Entities – Revenue Recognition The CEPI Forgivable Loan Funding provides the Company access to up to $142.5 million in funds to be used in connection with the potential commercial manufacture of NVX-CoV2373. As of June 30, 2020, the Company received $76.0 million of such funding. Under the funding agreements, the Company is only required to repay the CEPI Forgivable Loan Funding if the proceeds of sales to one or more third parties of NVX-CoV2373 cover the Company’s costs of manufacturing such vaccine, not including manufacturing costs funded by CEPI. As the financial risk remains with CEPI, the Company has determined that the use of the CEPI Forgivable Loan Funding is outside the scope of ASC 470, Debt. Research and Development The Company has determined that payments received under these agreements should be recorded as revenue rather than a reduction to research and development expenses. In reaching this determination that such payments should be recorded as revenue, management considered a number of factors, including whether the Company is principal under the arrangement, and whether the arrangement is significant to, and part of, the Company’s core operations. Further, management has consistently applied its policy of presenting such amounts as revenue. Net Loss per Share Net loss per share is computed using the weighted average number of shares of common stock outstanding. At June 30, 2020 and 2019, the Company had outstanding stock options, stock appreciation rights (“SARs”) and unvested restricted stock units (“RSUs”) totaling 7,797,651 and 2,935,847, respectively. In addition, at June 30, 2020, the Company had 438,885 shares outstanding of its newly designated Series A Convertible Preferred Stock , which are convertible into 4,388,850 shares of the Company’s common stock. At June 30, 2020, the Company’s Notes (see Note 7) would have been convertible into approximately 2,385,800 shares of the Company’s common stock assuming a common stock price of $136.20 or higher. These and any shares due to the Company upon settlement of its capped call transactions are excluded from the computation, as their effect is antidilutive. Recent Accounting Pronouncements Recently Adopted In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350)

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2020
Fair Value Measurements
Fair Value Measurements	Note 3 – Fair Value Measurements The following table represents the Company's fair value hierarchy for its financial assets and liabilities measured at fair value (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value at June 30, 2020 ​ Fair Value at December 31, 2019 ​ Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets ​ ​ ​ ​ ​ ​ Money market funds(1) ​ $ 225,373 ​ $ — ​ $ — ​ $ 42,960 ​ $ — ​ $ — Asset-backed securities(2) ​ — ​ 24,250 ​ — ​ — ​ 20,000 ​ — Treasury bills(3) ​ ​ — ​ ​ 99,972 ​ ​ — ​ ​ — ​ ​ — ​ ​ — Corporate debt securities ​ ― ​ 27,919 ​ — ​ — ​ — ​ — Total assets ​ $ 225,373 ​ $ 152,141 ​ $ — ​ $ 42,960 ​ $ 20,000 ​ $ — Liabilities ​ ​ ​ ​ ​ ​ ​ ​ Convertible notes payable ​ $ — ​ $ 309,166 ​ $ — ​ $ — ​ $ 125,811 ​ $ — (1) Classified as cash and cash equivalents as of June 30, 2020 and December 31, 2019, respectively, on the consolidated balance sheets. (2) Includes $24,250 and $20,000 classified as cash and cash equivalents as of June 30, 2020 and December 31, 2019, respectively, on the consolidated balance sheets. (3) Includes $49,989 classified as cash and cash equivalents as of June 30, 2020 on the consolidated balance sheets. ​ Fixed-income investments categorized as Level 2 are valued at the custodian bank by a third-party pricing vendor's valuation models that use verifiable observable market data, e.g., interest rates and yield curves observable at commonly quoted intervals and credit spreads, bids provided by brokers or dealers or quoted prices of securities with similar characteristics. Pricing of the Company's Notes (see Note 7) has been estimated using other observable inputs, including the price of the Company's common stock, implied volatility, interest rates and credit spreads among others. During the six months ended June 30, 2020 and 2019, the Company did not have any transfers between levels . The amount recorded in the Company's unaudited consolidated balance sheets for accounts payable and accrued expenses approximates its fair value due to its short-term nature.

Marketable Securities

Marketable Securities	6 Months Ended
	Jun. 30, 2020
Marketable Securities
Marketable Securities	Note 4 – Marketable Securities Marketable securities classified as available-for-sale as of June 30, 2020 and December 31, 2019 were comprised of (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2020 ​ December 31, 2019 ​ ​ ​ Gross Gross ​ ​ ​ ​ Gross Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ ​ ​ ​ ​ Cost ​ Gains ​ Losses ​ Fair Value ​ Cost ​ Gains ​ Losses ​ Fair Value Treasury bills ​ $ 49,981 ​ $ 2 ​ $ — ​ $ 49,983 ​ $ — ​ $ — ​ $ — ​ $ — Corporate debt securities ​ $ 27,877 ​ $ 42 ​ $ — ​ $ 27,919 ​ $ — ​ $ — ​ $ — ​ $ — Total ​ $ 77,858 ​ $ 44 ​ $ — ​ $ 77,902 ​ $ — ​ $ — ​ $ — ​ $ — ​ The primary objective of the Company's investment policy is the preservation of capital; thus, the Company's investment policy limits investments to certain types of instruments with high-grade credit ratings, places restrictions on maturities and concentrations in certain industries and requires the Company to maintain a certain level of liquidity.

Acquisition of Praha Vaccines a

Acquisition of Praha Vaccines a.s.	6 Months Ended
	Jun. 30, 2020
Acquisition of Praha Vaccines a.s.
Acquisition of Praha Vaccines a.s.	Note 5 – Acquisition of Praha Vaccines a.s. On May 27, 2020 (the “Acquisition Date”), the Company entered into a Share Purchase Agreement (the “Deed”) by and among Novavax AB, the Company’s wholly-owned Swedish subsidiary (the “Buyer”), and De Bilt Holdings B.V., Poonawalla Science Park B.V., and Bilthoven Biologicals B.V. (collectively, the “Sellers”) and, solely as guarantors, each of Serum International B.V. and the Company. Pursuant to the terms and conditions of the Deed, the Buyer acquired all the issued and outstanding shares of Praha Vaccines a.s., a vaccine manufacturing company, organized and existing under the laws of the Czech Republic (“Praha Vaccines”), from the Sellers for approximately €151.7 million (approximately $167.3 million) in cash (the “Purchase Price”), subject to customary working capital adjustments (collectively, the “Acquisition”), which have not been finalized. The assets of Praha Vaccines acquired as part of the Acquisition include a biologics manufacturing facility and associated assets in Bohumil, Czech Republic and will be used by the Company to expand its manufacturing capacity. The Purchase Price includes €10.0 million (approximately $11.1 million), which has been placed in an escrow account until September 30, 2020, less any amounts to settle claims made by the Buyer against the Sellers under the Deed or other ancillary agreements. The Deed and ancillary agreements contain customary warranties and post-completion covenants, as well as indemnities by each of the parties thereto. Preliminary Allocation of Purchase Price to Assets Acquired and Liabilities Assumed The Company has accounted for the Acquisition as a business combination using the acquisition method of accounting, with the Company as the acquirer. The acquisition method requires the Company to record the assets acquired and liabilities assumed at fair value. The amount by which the purchase price exceeds the fair value of net assets acquired is recorded as goodwill. The Company has commenced the appraisal process necessary to assess the fair values of the assets acquired and liabilities assumed to determine the amount of goodwill to be recognized as of the Acquisition Date. These appraisals are not yet complete and therefore, the amounts recorded for certain assets and liabilities are preliminary and are subject to adjustment as additional information is obtained about the facts and circumstances that existed as of the Acquisition Date. The final determination of the fair value of certain assets and liabilities will be completed within the measurement period of up to one year from the Acquisition Date. The final values may also result in changes to depreciation and amortization expense related to certain assets such as buildings and equipment. Any potential adjustments made could be material in relation to the preliminary values presented in the table below. The table below summarizes the preliminary allocation of the Purchase Price based upon the fair values of assets acquired and liabilities assumed at the Acquisition Date. The preliminary allocation is based upon information that was available to management at the time the consolidated financial statements were prepared and is subject to change prior to completion of the measurement period (in thousands): ​ ​ ​ ​ ​ Prepaid expense and other current assets $ 326 Property and equipment ​ 96,739 Goodwill ​ 70,468 Accounts payable ​ (1,193) Accrued expenses ​ (205) Other non-current liabilities ​ (813) Purchase Price, net of cash acquired ​ $ 165,322 ​ The fair value of the assets acquired and liabilities assumed were preliminarily determined using market and cost valuation methodologies. The fair value measurements are based on significant unobservable inputs that were developed by the Company using publicly available information, market participant assumptions, and cost and development assumptions. Because of the use of significant unobservable inputs, the fair value measurements represent a Level 3 measurement as defined in ASC 820, Fair Value Measurement and Disclosures The cost approach was the primary approach used to value fixed assets, including the real property. Fixed assets are depreciated on a straight-line basis over their expected remaining useful lives, ranging from 4 The Company recorded $70.5 million in goodwill related to the Acquisition representing the Purchase Price that was in excess of the fair value of the assets acquired and liabilities assumed. The goodwill generated from the Acquisition is not expected to be deductible for U.S. federal income tax purposes. The goodwill recognized is attributable to intangible assets that do not qualify for separate recognition, such as the assembled workforce of Praha Vaccines. Current assets and current liabilities were recorded at their contractual or historical acquisition amounts, which approximate their fair value. Determining the fair value of assets acquired and liabilities assumed requires the exercise of significant professional judgment. Use of different estimates and judgments could yield different results. Impact to Financial Results for the Three and Six Months Ended June 30, 2020 The results of operations from Praha Vaccines have been included in the consolidated financial statements since the Acquisition Date. As a result, the consolidated financial results for the three and six months ended June 30, 2020 do not reflect a full three months and six months of Praha Vaccines results, respectively. From the Acquisition Date through June 30, 2020, Praha Vaccines has not recognized any revenue and recorded a net income of $1.8 million from Praha Vaccines’ operations. The Company incurred approximately $1.9 million of costs related to the Acquisition in the three months ended June 30, 2020, which are included within general and administrative expenses in the consolidated statements of operations. Supplemental Pro Forma Financial Information (Unaudited) The unaudited pro forma financial information for the periods set forth below gives effect to the Acquisition as if it had occurred as of January 1, 2019. The pro forma financial information is presented for informational purposes only and is not necessarily indicative of the results of operations that would have been achieved had the Acquisition been consummated as of that time. The unaudited pro forma financial information combines the historical results of operations of the Company and Praha Vaccines for the periods presented below and reflects the application of certain pro forma adjustments (in thousands, except per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 ​ 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 35,538 ​ $ 3,357 ​ $ 38,915 ​ $ 7,339 Net loss ​ (18,196) ​ (42,119) ​ (45,821) ​ (87,367) Basic and diluted net loss per share ​ (0.31) ​ (0.97) ​ (0.83) ​ (2.08) ​ Pro forma adjustments include the recognition of depreciation expense based on the Acquisition Date fair value and remaining useful lives of Praha Vaccines’ fixed assets (net of historical depreciation expense) and the elimination of costs related to the Acquisition, which are non-recurring in nature.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	6 Months Ended
	Jun. 30, 2020
Goodwill and Other Intangible Assets
Goodwill and Other Intangible Assets	Note 6 – Goodwill and Other Intangible Assets Goodwill The change in the carrying amounts of goodwill for the six months ended June 30, 2020 was as follows (in thousands): ​ ​ ​ ​ ​ ​ Amount Balance at December 31, 2019 ​ $ 51,154 Goodwill resulting from the acquisition of Praha Vaccines ​ ​ 70,468 Currency translation adjustments ​ (2,773) Balance at June 30, 2020 ​ $ 118,849 ​ Identifiable Intangible Assets Purchased intangible assets consisted of the following as of June 30, 2020 and December 31, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2020 ​ December 31, 2019 ​ Gross ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ ​ Carrying ​ Accumulated ​ Intangible ​ Carrying ​ Accumulated ​ Intangible ​ ​ Amount ​ Amortization ​ Assets, Net ​ Amount ​ Amortization ​ Assets, Net Finite-lived intangible assets: ​ ​ ​ ​ ​ ​ Proprietary adjuvant technology ​ $ 7,991 ​ $ (2,764) ​ $ 5,227 ​ $ 7,985 ​ $ (2,562) ​ $ 5,423 Collaboration agreements ​ 3,608 ​ (3,585) ​ 23 ​ 3,606 ​ (3,448) ​ 158 Total identifiable intangible assets ​ $ 11,599 ​ $ (6,349) ​ $ 5,250 ​ $ 11,591 ​ $ (6,010) ​ $ 5,581 ​ Amortization expense for the six months ended June 30, 2020 and 2019 was $0.3 million. Estimated amortization expense for existing intangible assets for the remainder of 2020 and for each of the five succeeding years ending December 31 will be as follows (in thousands): ​ ​ ​ ​ ​ Year Amount 2020 (remainder) ​ $ 222 2021 ​ 400 2022 ​ 400 2023 ​ 400 2024 ​ 400 2025 ​ 400 ​

Long-Term Debt

Long-Term Debt	6 Months Ended
	Jun. 30, 2020
Long-Term Debt
Long-Term Debt	Note 7 – Long-Term Debt Convertible Notes The Company incurred approximately $10.0 million of debt issuance costs during the first quarter of 2016 relating to the issuance of $325 million aggregate principal amount of convertible senior unsecured notes that will mature on February 1, 2023 (the “Notes”), which were recorded as a reduction to the Notes on the consolidated balance sheet. The $10.0 million of debt issuance costs is being amortized and recognized as additional interest expense over the seven-year contractual term of the Notes on a straight-line basis, which approximates the effective interest rate method. Total convertible notes payable consisted of the following at (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Principal amount of the Notes ​ $ 325,000 ​ $ 325,000 Unamortized debt issuance costs ​ (3,677) ​ (4,389) Total convertible notes payable ​ $ 321,323 ​ $ 320,611 ​ Interest expense incurred in connection with the Notes consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coupon interest at 3.75% ​ $ 3,047 ​ $ 3,047 ​ $ 6,094 ​ $ 6,094 Amortization of debt issuance costs ​ 356 ​ 356 ​ 712 ​ 712 Total interest expense on the Notes ​ $ 3,403 ​ $ 3,403 ​ $ 6,806 ​ $ 6,806 ​

Preferred Stock

Preferred Stock	6 Months Ended
	Jun. 30, 2020
Preferred Stock
Preferred Stock	Note 8 – Preferred Stock In June 2020, the Company entered into a redeemable Series A Convertible Preferred Stock Subscription Agreement (“Subscription Agreement”), pursuant to which the Company agreed to issue and sell in a private placement 438,885 shares of its newly designated redeemable Series A Convertible Preferred Stock, par value $0.01 per share (“Preferred Stock”), at a purchase price of $455.70 per share, for total gross proceeds of $200.0 million (the “Preferred Private Placement”). Under the terms of the Preferred Stock, any holder thereof has the right to redeem shares of the Preferred Stock at the original purchase price if the Company fails to meet certain SEC filing requirements and file and maintain for at least one year a registration statement for the resale of the shares of common stock underlying the Preferred Stock. Because certain of these features are outside of the Company's control, the Company has classified the Preferred Stock outside of permanent equity. Each share of Preferred Stock is convertible into ten shares of common stock. The conversion price is equal to $45.57 and is subject to adjustment based on standard anti-dilution provisions. Holders of Preferred Stock are not entitled to cumulative dividends, are not entitled to vote on matters submitted to common stockholders and have a liquidation preference over common stockholders equal to the greater of the original purchase price, plus declared and unpaid Preferred Stock dividends, and the amount that would be payable in respect of common stock assuming the Preferred Stock converted immediately prior to the liquidation. The Company recognized a beneficial conversion feature of approximately $24.1 million that was recorded within additional paid-in capital and accumulated deficit as the Preferred Stock issuance is only contingently redeemable and convertible at any time at the option of the holder.

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	6 Months Ended
	Jun. 30, 2020
Stockholders' Equity (Deficit)
Stockholders' Equity (Deficit)	Note 9 – Stockholders' Equity (Deficit) In June 2020, in advance of David M. Mott joining the Company’s Board of Directors, the Company agreed to sell 32,916 shares of common stock to him at a purchase price of $45.57 per share, reflecting the closing price of the Company’s common stock on the trading date prior to the date the parties’ agreement regarding the sale, for total gross proceeds of $1.5 million. Mr. Mott joined the Company’s Board of Directors later in the same month. In May 2020, the Company entered into an At Market Issuance Sales Agreement ("May 2020 Sales Agreement"), which allows it to issue and sell up to $250 million in gross proceeds of its common stock. During the six months ended June 30, 2020, the Company sold 2.2 million shares of common stock under the May 2020 Sales Agreement resulting in $107.0 million in net proceeds, leaving $141.6 million remaining under the May 2020 Sales Agreement. In March 2020, the Company entered into an At Market Issuance Sales Agreement (“March 2020 Sales Agreement”), which allowed it to issue and sell up to $150 million in gross proceeds of its common stock. During the six months ended June 30, 2020, the Company sold 8.6 million shares of common stock under the March 2020 Sales Agreement resulting in $148.1 million in net proceeds. The March 2020 Sales Agreement was fully utilized at that time. In January 2020, the Company entered into an At Market Issuance Sales Agreement ("January 2020 Sales Agreement"), which allowed it to issue and sell up to $100 million in gross proceeds of its common stock. During the first quarter of 2020, the Company sold 10.5 million shares of common stock under the January 2020 Sales Agreement resulting in $98.7 million in net proceeds. The January 2020 Sales Agreement was fully utilized at that time. In December 2018, the Company entered into an At Market Issuance Sales Agreement (“December 2018 Sales Agreement”), which allowed it to issue and sell up to $100 million in gross proceeds of its common stock. During the six months ended June 30, 2019, the Company sold 1.7 million shares of common stock under the December 2018 Sales Agreement, of which all were sold in the first quarter of 2019, resulting in $17.4 million in net proceeds. During the six months ended June 30, 2020, the Company sold 7.2 million shares of common stock under the December 2018 Sales Agreement, of which all were sold in the first quarter of 2020, resulting in $38.5 million in net proceeds. The December 2018 Sales Agreement was fully utilized at that time. In December 2017, the Company entered into an At Market Issuance Sales Agreement (“December 2017 Sales Agreement”), which allowed it to issue and sell up to $75 million in gross proceeds of its common stock. During the six months ended June 30, 2019, the Company sold 2.5 million shares of common stock under the December 2017 Sales Agreement, of which all were sold in the first quarter of 2019, resulting in $37.9 million in net proceeds. The December 2017 Sales Agreement was fully utilized at that time.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2020
Stock-Based Compensation
Stock-Based Compensation	Note 10 – Stock-Based Compensation Stock Options The 2015 Stock Incentive Plan, as amended (“2015 Plan”), was approved at the Company's annual meeting of stockholders in June 2015. Under the 2015 Plan, equity awards may be granted to officers, directors, employees and consultants of and advisors to the Company and any present or future subsidiary. The 2015 Plan authorizes the issuance of up to 10,900,000 shares of common stock under equity awards granted under the 2015 Plan, which includes an increase of 7,100,000 shares approved for issuance under the 2015 Plan at the Company's 2020 annual meeting of stockholders. All such shares authorized for issuance under the 2015 Plan have been reserved. The 2015 Plan will expire on March 4, 2025. The Amended and Restated 2005 Stock Incentive Plan (“2005 Plan”) expired in February 2015 and no new awards may be made under such plan, although awards will continue to be outstanding in accordance with their terms. The 2015 Plan permits and the 2005 Plan permitted the grant of stock options (including incentive stock options), restricted stock, stock appreciation rights and restricted stock units. In addition, under the 2015 Plan, unrestricted stock, stock units and performance awards may be granted. Stock options and stock appreciation rights generally have a maximum term of 10 years and may be or were granted with an exercise price that is no less than 100% of the fair market value of the Company's common stock at the time of grant. Grants of stock options are generally subject to vesting over periods ranging from one Stock Options and Stock Appreciation Rights The following is a summary of stock options and stock appreciation rights activity under the 2015 Plan and 2005 Plan for the six months ended June 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2015 Plan ​ 2005 Plan ​ ​ Weighted- ​ Weighted- ​ ​ ​ ​ Average ​ ​ ​ Average ​ ​ Stock Options ​ Exercise Price ​ Stock Options ​ Exercise Price Outstanding at January 1, 2020 3,388,701 ​ $ 35.64 501,780 ​ $ 64.19 Granted 2,820,041 ​ $ 22.28 — ​ $ — Exercised (209,959) ​ $ 30.35 (76,856) ​ $ 33.56 Canceled (32,254) ​ $ 41.18 (22,329) ​ $ 52.26 Outstanding at June 30, 2020 5,966,529 ​ $ 29.50 402,595 ​ $ 70.71 Shares exercisable at June 30, 2020 953,073 ​ $ 85.48 402,595 ​ $ 70.71 Shares available for grant at June 30, 2020 3,098,569 ​ ​ ​ In 2019, the Company granted 192,400 stock appreciation rights, with a weighted-average exercise price of $5.95, under the 2015 Plan. Additionally, in 2019, due to limitations on the equity awards available under the 2015 Plan, the Company granted to certain employees 1,014,200 stock options, with a weighted-average exercise price of $5.95, under the 2015 Plan that were subject to approval of an increase in the number of shares under the 2015 Plan at the Company's 2020 annual meeting of stockholders. Furthermore, in April 2020, due to limitations on the equity awards available under the 2015 Plan, the Company granted to all of its employees collectively 2,501,600 stock options, with a weighted-average exercise price of $19.08, and 326,050 restricted stock units under the 2015 Plan that include a performance requirement related to its NVX-CoV2373 program that were also subject to approval of an increase in the number of shares under the 2015 Plan at the Company's 2020 annual meeting of stockholders. Since the proposal to increase the number of shares under the 2015 Plan was approved at the Company’s 2020 annual meeting of stockholders, as discussed in the “ Stock Options ​ The fair value of stock options granted under the 2015 Plan was estimated at the date of grant or the date upon which the 2015 Plan was approved by the Company’s stockholders for stock options discussed above using the Black-Scholes option-pricing model with the following assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average Black-Scholes fair value of stock options granted ​ $77.41 ​ ​ $8.50 ​ $76.99 ​ ​ $23.43 ​ Risk-free interest rate ​ 0.3%-0.6% ​ ​ 1.8%-2.3% ​ ​ 0.3%-1.5% ​ ​ 1.8%-2.6% ​ Dividend yield ​ 0% ​ ​ 0% ​ ​ 0% ​ ​ 0% ​ Volatility ​ 116.0%-151.5% ​ ​ 127.3%-128.5% ​ ​ 116.0%-151.5% ​ ​ 111.6%-128.5% ​ Expected term (in years) ​ 3.9-7.6 ​ ​ 4.0 ​ 3.9-7.6 ​ ​ 4.0-4.5 ​ Expected forfeiture rate ​ 0% ​ ​ 0% ​ ​ 0% ​ ​ 0% ​ ​ The total aggregate intrinsic value and weighted-average remaining contractual term of stock options and stock appreciation rights outstanding under the 2015 Plan and 2005 2020 2005 2020 Employee Stock Purchase Plan The Employee Stock Purchase Plan, as amended (the “ESPP”), was approved at the Company's annual meeting of stockholders in June 2013. The ESPP currently authorizes an aggregate of 600,000 shares of common stock to be purchased. The ESPP allows employees to purchase shares of common stock of the Company at each purchase date through payroll deductions of up to a maximum of 15% of their compensation, at 85% of the lesser of the market price of the shares at the time of purchase or the market price on the beginning date of an option period (or, if later, the date during the option period when the employee was first eligible to participate). At June 30, 2020, there were 278,543 shares available for issuance under the ESPP. The ESPP is considered compensatory for financial reporting purposes. As such, the fair value of ESPP shares was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 Range of Black-Scholes fair value of ESPP shares granted ​ ​ $2.87-$21.80 ​ ​ $9.45-$34.78 ​ $2.57-$35.00 ​ ​ $7.25-$34.78 Risk-free interest rate ​ 1.5%-2.6% ​ ​ 1.3%-2.5% ​ ​ 1.5%-2.6% ​ ​ 1.2%-2.5% Dividend yield ​ 0% ​ 0% ​ 0% ​ 0% Volatility ​ 66.6%-150.9% ​ ​ 59.7%-171.6% ​ ​ 66.6%-154.4% ​ ​ 52.2%-171.6% Expected term (in years) ​ 0.5-2.0 ​ ​ 0.5-2.0 ​ ​ 0.5-2.0 ​ ​ 0.5-2.0 Expected forfeiture rate ​ 0% ​ 0% ​ 0% ​ 0% ​ Restricted Stock Units The following is a summary of restricted stock units activity for the six months ended June 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ Per Share ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ Number of ​ Grant-Date ​ ​ Shares ​ Fair Value Outstanding and Unvested at January 1, 2020 1,102,311 ​ $ 5.95 Restricted stock units granted 457,204 ​ $ 75.97 Restricted stock units vested (47,563) ​ $ 18.61 Restricted stock units forfeited (29,425) ​ $ 25.46 Outstanding and Unvested at June 30, 2020 1,482,527 ​ $ 26.75 ​ The Company recorded all stock-based compensation expense in the consolidated statements of operations as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 Research and development ​ $ 4,098 ​ $ 2,444 ​ $ 6,005 ​ $ 5,624 General and administrative ​ 3,834 ​ 2,176 ​ 5,892 ​ 4,555 Total stock-based compensation expense ​ $ 7,932 ​ $ 4,620 ​ $ 11,897 ​ $ 10,179 ​ As of June 30, 2020, there was approximately $344 million of total unrecognized compensation expense related to unvested stock options, stock appreciation rights, restricted stock units and the ESPP. The increase in unrecognized compensation expense is primarily due to the awards that were subject to approval of an increase in the number of shares under the 2015 Plan at the Company's 2020 annual meeting of stockholders, as discussed in the " Stock Options

U.S. Government Agreements, Gra

U.S. Government Agreements, Grants and Licenses	6 Months Ended
	Jun. 30, 2020
U.S. Government Agreements, Grants and Licenses
U.S. Government Agreements, Grants and Licenses	Note 11 – U.S. Government Agreements, Grants and Licenses Operation Warp Speed In July 2020, the Company entered into a Project Agreement (the “Project Agreement”) with Advanced Technology International, Inc. (“ATI”), the Consortium Management Firm acting on behalf of the Medical CBRN Defense Consortium in connection with Operation Warp Speed (“OWS”). OWS is a partnership among components of the U.S. Department of Health and Human Services and the U.S. Department of Defense working to accelerate the development, manufacturing and distribution of COVID-19 vaccines, therapeutics and diagnostics. The Project Agreement relates to the Base Agreement the Company entered into with ATI in June 2020 (the “Base Agreement”, together with the Project Agreement, the “OWS Agreement”). Under the OWS Agreement, the Company is entitled to receive funding of up to $1.6 billion to support certain activities related to the development of NVX-CoV2373 and the manufacture and delivery of the vaccine candidate to the U.S. Government. Pursuant to the OWS Agreement, the Company is currently authorized to make expenditures or incur obligations of up to $800 million, and the parties have committed to negotiate a definitive agreement by December 2020 that provides for aggregate costs payable to the Company up to but not in excess of the approved budget of $1.6 billion. If the parties have not agreed on definitive pricing or other terms by December 2020, or any extension of such target date granted by the U.S. Government, the U.S. Government has the discretion to unilaterally determine a fair and reasonable price for completion of the definitive agreement. The OWS Agreement requires the Company to conduct certain clinical, regulatory and other activities, including a pivotal Phase 3 clinical trial to determine the safety and efficacy of NVX-CoV2373, and to manufacture and deliver to the U.S. Government 100 million doses of the vaccine candidate. Funding under the OWS Agreement is payable to the Company for various development, clinical trial, manufacturing, regulatory and other activities. The OWS Agreement contains terms and conditions that are customary for U.S. Government agreements of this nature, including provisions giving the U.S. Government the right to terminate the Base Agreement and/or the Project Agreement based on a reasonable determination that the funded project will not produce beneficial results commensurate with the expenditure of resources and that termination would be in the U.S. Government’s interest. If the Project Agreement is terminated prior to completion, the Company is entitled to be paid for work performed and costs or obligations incurred prior to termination and consistent with the terms of the OWS Agreement. The performance period under the Project Agreement extends from July 2020 through December 2021, subject to early termination by the U.S. Government or extension by mutual agreement of the parties. U.S. Department of Defense In June 2020, the Company entered into a letter contract (the “DoD Contract”) with the U.S. Department of Defense (the “DoD”) Joint Program Executive Office for Chemical, Biological, Radiological and Nuclear Defense (“JPEO-CRBND-EB”), under which JPEO-CRBND-EB agreed to provide funding of up to $60.0 million to the Company to support the manufacture of NVX-CoV2373. Under the DoD Contract, the Company is currently authorized to make expenditures or incur obligations up to $22.0 million, and the Company and the DoD have committed to negotiate a definitive cost-reimbursement contract by December 2020 that provides for costs payable by the DoD not to exceed $60.0 million. If the Company and the DoD have not agreed on pricing or terms by December 2020, or any extension of such target date granted by the DoD, the DoD has the discretion to determine a reasonable price or fee for completion of the contract. Under the DoD Contract, the Company is expected to deliver 10 million doses of NVX-CoV2373 to the DoD in the fourth quarter of 2020. The 10 million doses of NVX-CoV2373 may be used in Phase 2/3 clinical trials or under an Emergency Use Authorization, if approved by the U.S. Food and Drug Administration (“FDA”). Pursuant to the DoD Contract, if NVX-CoV2373 is approved by the FDA, the DoD is entitled to most-favored customer status for a period of five years from the award of the DoD Contract, meaning that the Company cannot give any comparable commercial client in the United States more favorable pricing than the DoD under similar transactional circumstances. During the three months ended June 30, 2020, the Company recognized revenue from the DoD Contract of $0.3 million. Coalition for Epidemic Preparedness Innovations In May 2020, the Company entered into a restated funding agreement (the “CEPI Funding Agreement”) with CEPI, under which CEPI agreed to provide funding of up to $384.5 million to the Company to support the development of NVX-CoV2373, in addition to the $3.9 million of funding CEPI provided to the Company pursuant to an initial funding agreement entered into between the Company and CEPI in March 2020. The CEPI Funding Agreement provides up to $245.9 million in Grant Funding and up to $142.5 million in Forgivable Loan Funding, which loans are in the form of one or more forgivable no interest term loans in order to prepay certain manufacturing activities and are not subject to restrictive or financial covenants. The Company is only required to repay any CEPI Forgivable Loan Funding under certain circumstances to the extent it sells doses of NVX-CoV2373, produced with the funds provided and included in such loan(s), to a third party. Under the terms of the CEPI Funding Agreement, among other things, the Company and CEPI agreed on the importance of global equitable access to any vaccines produced pursuant to the CEPI Funding Agreement. Any such vaccines, if approved, are expected to be procured and allocated through global mechanisms under discussion as part of the Access to COVID-19 Tools (ACT) Accelerator, an international initiative launched by the World Health Organization (“WHO”), Gavi the Vaccine Alliance, CEPI and other global non-governmental organizations and governmental leaders in 2020. The scope and continuation of the CEPI Funding Agreement may be modified depending on ongoing developments of the COVID-19 outbreak and the success of NVX-CoV2373 relative to other third-party COVID-19 vaccine candidates or treatments. If the WHO, CEPI or a regulatory authority having jurisdiction over a clinical trial of NVX-CoV2373 determines that a third-party product candidate has substantially greater potential than a Company vaccine product, the Company must cease its clinical trial in the relevant region, and will be reimbursed for any costs incurred as a result thereof. In addition, CEPI has the right to unilaterally terminate the CEPI Funding Agreement if CEPI reasonably determines that (i) there are material safety, regulatory or ethical issues with the development of NVX-CoV2373, (ii) NVX-CoV2373 development should be limited in scope or terminated, (iii) the Company becomes unable to discharge its obligations under the agreement, (iv) the Company fails to meet certain milestones, or (v) the Company commits fraud or a financial irregularity. Payments received in advance that are related to future performance are deferred and recognized as revenue when the research and development activities are performed. Cash payments received under the funding agreements are restricted as to their use until expenditures contemplated in the funding agreements are incurred. During the three and six months ended June 30, 2020, the Company recognized revenue from the funding agreements of $34.2 million and $36.5 million, respectively. Bill & Melinda Gates Foundation In support of the Company's development of ResVax TM five Payments received in advance that are related to future performance are deferred and recognized as revenue when the research and development activities are performed. Cash payments received under the BMGF Grant Agreement are restricted as to their use until expenditures contemplated in the BMGF Grant Agreement are incurred. During the three and six months ended June 30, 2020, the Company recognized revenue from the Grant of $0.2 million and $0.4 million, respectively, and has recognized approximately $82 million in revenue since the inception of the agreement. Serum Institute of India Private Limited In July 2020, the Company entered into a supply and license agreement with Serum Institute of India Private Limited (“SIIPL”), under which it granted exclusive and non-exclusive licenses to SIIPL for the development, co-formulation, filling and finishing, registration and commercialization by SIIPL of NVX-CoV2373. SIIPL agreed to purchase the two vaccine components (the antigen drug substance and the Matrix-M adjuvant) from the Company and the parties will equally split the revenue from sale of such product by SIIPL in its licensed territory, net of agreed costs. The Company granted to SIIPL (i) an exclusive license in India during the agreement, and (ii) a non-exclusive license (a) during the “Pandemic Period” (as declared by the World Health Organization), in all countries other than specified countries designated by the World Bank as upper-middle or high-income countries, with respect to which the Company retains rights, and (b) after the Pandemic Period, in only those countries designated as low or middle-income by the World Bank. Following the Pandemic Period, the Company may notify SIIPL of any bona fide opportunities for the Company to license the product to a third party in such low and middle-income countries and SIIPL would have an opportunity to match or improve such third party terms, failing which, the Company would have the discretion to remove one or more non-exclusive countries from SIIPL’s license. Takeda Pharmaceutical Company Limited In August 2020, the Company announced a partnership with Takeda Pharmaceutical Company Limited (“Takeda”) for the exclusive development, manufacturing and commercialization of NVX-CoV2373 in Japan. Takeda will receive funding from the Government of Japan’s Ministry of Health, Labour and Welfare to support the technology transfer, establishment of infrastructure and scale-up of manufacturing. The Company anticipates that Takeda has manufacturing capacity of over 250 million doses per year. The Company will be entitled to receive payments based on the achievement of certain development and commercial milestones, as well as a portion of proceeds from the sale of the vaccine. At June 30, 2020, the Company's current restricted cash and deferred revenue balances on the consolidated balance sheet include its estimate of costs to be reimbursed and revenue to be recognized, respectively, in the next twelve months under the CEPI Funding Agreement and BMGF Grant Agreement.

CARES Act

CARES Act	6 Months Ended
	Jun. 30, 2020
CARES Act	Note 12 - CARES Act On March 27, 2020, Congress enacted the Coronavirus Aid, Relief and Economic Security Act ("CARES Act") to provide certain relief as a result of the COVID-19 pandemic. Amongst other items, the CARES Act lifts certain interest expense deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017. The enactment of the CARES Act did not result in any material adjustments to the Company's income tax provision or net deferred tax assets for the six months ended June 30, 2020.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. The consolidated balance sheet as of June 30, 2020, the consolidated statements of operations and the consolidated statements of comprehensive loss for the three and six months ended June 30, 2020 and 2019, the consolidated statements of changes in stockholders’ equity (deficit) for the three and six months ended June 30, 2020 and 2019 and the consolidated statements of cash flows for the six months ended June 30, 2020 and 2019 are unaudited, but include all adjustments (consisting of normal recurring adjustments) that the Company considers necessary for a fair presentation of the financial position, operating results, comprehensive loss, changes in stockholders’ equity (deficit) and cash flows, respectively, for the periods presented. Although the Company believes that the disclosures in these unaudited consolidated financial statements are adequate to make the information presented not misleading, certain information and footnote information normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted as permitted under the rules and regulations of the United States Securities and Exchange Commission (“SEC”). The unaudited consolidated financial statements include the accounts of Novavax, Inc. and its wholly owned subsidiaries, Novavax AB and Praha Vaccines a.s. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying unaudited consolidated financial statements are presented in U.S. dollars. The functional currency of Novavax AB, which is located in Sweden, is the local currency (Swedish Krona), and the functional currency of Praha Vaccines a.s., which is located in the Czech Republic, is the local currency (Czech Koruna). The translation of assets and liabilities of these subsidiaries to U.S. dollars is made at the exchange rate in effect at the consolidated balance sheet date, while equity accounts are translated at historical rates. The translation of the statement of operations data is made at the average exchange rate in effect for the period. The translation of operating cash flow data is made at the average exchange rate in effect for the period, and investing and financing cash flow data is translated at the exchange rate in effect at the date of the underlying transaction. Translation gains and losses are recognized as a component of accumulated other comprehensive loss in the accompanying unaudited consolidated balance sheets. The foreign currency translation adjustment balance included in accumulated other comprehensive loss was $13.2 million and $12.5 million at June 30, 2020 and December 31, 2019, respectively. The accompanying unaudited consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019. Results for this or any interim period are not necessarily indicative of results for any future interim period or for the entire year. The Company operates in one business segment.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ materially from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of highly liquid investments with maturities of three months or less from the date of purchase. Cash and cash equivalents consist of the following at (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Cash ​ $ 124,783 ​ $ 15,863 Money market funds ​ 225,373 ​ 42,960 Asset-backed securities ​ 24,250 ​ 20,000 Treasury bills ​ 49,989 ​ — Cash and cash equivalents ​ $ 424,395 ​ $ 78,823 ​ Cash equivalents are recorded at cost, which approximate fair value due to their short-term nature.
Marketable Securities	Marketable Securities Marketable securities consist of debt securities with maturities greater than three months from the date of purchase that include commercial paper, asset-backed securities, treasury bills and corporate notes. Classification of marketable securities between current and non-current is dependent upon the maturity date at the balance sheet date taking into consideration the Company's ability and intent to hold the investment to maturity. Interest and dividend income are recorded when earned and included in investment income in the consolidated statements of operations. Premiums and discounts, if any, on marketable securities are amortized or accreted to maturity and included in investment income in the consolidated statements of operations. The specific identification method is used in computing realized gains and losses on the sale of the Company's securities. The Company classifies its marketable securities with readily determinable fair values as “available-for-sale.” Investments in securities that are classified as available-for-sale are measured at fair market value in the consolidated balance sheets, and unrealized gains and losses on marketable securities are reported as a separate component of stockholders' deficit until realized. Marketable securities are evaluated periodically to determine whether a decline in value is “other-than-temporary.” The term “other-than-temporary” is not intended to indicate a permanent decline in value. Rather, it means that the prospects for a near term recovery of value are not necessarily favorable, or that there is a lack of evidence to support fair values equal to, or greater than, the carrying value of the security. Management reviews criteria, such as the magnitude and duration of the decline, as well as the Company's ability to hold the securities, including whether the Company will be required to sell a security prior to recovery of its amortized cost basis, the investment issuer's financial condition and business outlook to predict whether the loss in value is other-than-temporary. If a decline in value is determined to be other-than-temporary, the value of the security is reduced and the impairment is recorded as other income (expense) in the consolidated statements of operations.
Restricted Cash	Restricted Cash The Company’s current and non-current restricted cash includes payments received under the Coalition for Epidemic Preparedness Innovations (“CEPI”) funding agreements (see Note 11), payments received under the Bill & Melinda Gates Foundation (“BMGF”) grant agreement (see Note 11), escrow funds paid in connection with the acquisition of Praha Vaccines a.s. (see Note 5) and funds received in connection with a transaction in 2019 with Catalent Maryland, Inc. (formerly Paragon Bioservices, Inc.), a unit of Catalent Biologics (“Catalent”), pursuant to which the Company agreed to sell to Catalent certain assets related to its biomanufacturing and development activities and cash collateral accounts under letters of credit that serve as security deposits for certain facility leases. The Company will utilize the CEPI and BMGF funds as it incurs expenses for services performed under these agreements. At both June 30, 2020 and December 31, 2019, the restricted cash balances (both current and non-current) consisted of $1.4 million of payments received from BMGF, $1.5 million held in escrow received in connection with the Catalent transaction and $0.4 million of security deposits. At June 30, 2020, the restricted cash balance also included $92.6 million of payments under the CEPI funding agreements and $11.2 million held in escrow that was paid by the Company in connection with the Praha Vaccines a.s. acquisition. The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the statement of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Cash and cash equivalents ​ $ 424,395 ​ $ 78,823 Restricted cash current ​ 106,768 ​ 2,947 Restricted cash non-current ​ 411 ​ 410 Cash, cash equivalents and restricted cash ​ $ 531,574 ​ $ 82,180
Acquisitions	Acquisitions The Company applies the acquisition method of accounting to business combinations in accordance with ASC 805, Business Combinations. The Company’s consolidated financial statements include the operating results of an acquired entity from the date on which it obtains control of the business acquired. The Company recognizes and measures the identifiable assets acquired and liabilities assumed, as of the acquisition date, based on their estimated fair value with the excess purchase consideration, if any, recognized as goodwill. In determining fair value, the Company uses various recognized valuation methods, including the cost and market approaches. The Company initially performs these valuations based on preliminary estimates and assumptions by management or independent valuation specialists under Company supervision, where appropriate, and makes revisions as estimates and assumptions are finalized. The final determination of fair values must be completed no later than the first anniversary of the date of acquisition. The Company expenses acquisition related costs as incurred. See Note 5 for further discussion around the Company’s recent acquisition of Praha Vaccines a.s.
Revenue Recognition	Revenue Recognition The Company performs research and development under grant, license and clinical development agreements. Payments received in advance of work performed are recorded as deferred revenue. The Company entered into funding agreements with CEPI that provide total funding of up to $388.4 million (see Note 11). The funding includes approximately $245.9 million in the form of a grant (“CEPI Grant Funding”) and up to $142.5 million in the form of one or more forgivable no interest term loans (“CEPI Forgivable Loan Funding”). Under the CEPI Grant Funding, the Company is entitled to reimbursement for costs that support development activities of NVX-CoV2373. The CEPI Forgivable Loan Funding is designated for the prepayment of certain manufacturing activities. The funding from CEPI is critical to enable ongoing development of NVX-CoV2373, and to enable the Company to obtain product licensing to produce the vaccine for use in clinical trials and commercial distribution, if approved. The CEPI funding agreements do not provide a direct economic benefit to CEPI. Rather, the Company entered into an agreement with CEPI to attempt to develop a COVID-19 vaccine under which CEPI only benefits to the extent the arrangement furthers its public health mission. Based on these circumstances, the Company does not consider CEPI to be a customer and concluded the funding agreements are outside the scope of ASC 606, Revenue from Contracts with Customers Not-for-Profit Entities – Revenue Recognition The CEPI Forgivable Loan Funding provides the Company access to up to $142.5 million in funds to be used in connection with the potential commercial manufacture of NVX-CoV2373. As of June 30, 2020, the Company received $76.0 million of such funding. Under the funding agreements, the Company is only required to repay the CEPI Forgivable Loan Funding if the proceeds of sales to one or more third parties of NVX-CoV2373 cover the Company’s costs of manufacturing such vaccine, not including manufacturing costs funded by CEPI. As the financial risk remains with CEPI, the Company has determined that the use of the CEPI Forgivable Loan Funding is outside the scope of ASC 470, Debt. Research and Development The Company has determined that payments received under these agreements should be recorded as revenue rather than a reduction to research and development expenses. In reaching this determination that such payments should be recorded as revenue, management considered a number of factors, including whether the Company is principal under the arrangement, and whether the arrangement is significant to, and part of, the Company’s core operations. Further, management has consistently applied its policy of presenting such amounts as revenue.
Net Loss per Share	Net Loss per Share Net loss per share is computed using the weighted average number of shares of common stock outstanding. At June 30, 2020 and 2019, the Company had outstanding stock options, stock appreciation rights (“SARs”) and unvested restricted stock units (“RSUs”) totaling 7,797,651 and 2,935,847, respectively. In addition, at June 30, 2020, the Company had 438,885 shares outstanding of its newly designated Series A Convertible Preferred Stock , which are convertible into 4,388,850 shares of the Company’s common stock. At June 30, 2020, the Company’s Notes (see Note 7) would have been convertible into approximately 2,385,800 shares of the Company’s common stock assuming a common stock price of $136.20 or higher. These and any shares due to the Company upon settlement of its capped call transactions are excluded from the computation, as their effect is antidilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted In January 2017, the FASB issued ASU No. 2017-04, Intangibles-Goodwill and Other (Topic 350)

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2020
Summary of Significant Accounting Policies
Schedule of cash and cash equivalents	Cash and cash equivalents consist of highly liquid investments with maturities of three months or less from the date of purchase. Cash and cash equivalents consist of the following at (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Cash ​ $ 124,783 ​ $ 15,863 Money market funds ​ 225,373 ​ 42,960 Asset-backed securities ​ 24,250 ​ 20,000 Treasury bills ​ 49,989 ​ — Cash and cash equivalents ​ $ 424,395 ​ $ 78,823
Schedule of reconciliation of cash, cash equivalents and restricted cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total of the same such amounts shown in the statement of cash flows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Cash and cash equivalents ​ $ 424,395 ​ $ 78,823 Restricted cash current ​ 106,768 ​ 2,947 Restricted cash non-current ​ 411 ​ 410 Cash, cash equivalents and restricted cash ​ $ 531,574 ​ $ 82,180

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
Fair Value Measurements
Schedule of fair value hierarchy	The following table represents the Company's fair value hierarchy for its financial assets and liabilities measured at fair value (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fair Value at June 30, 2020 ​ Fair Value at December 31, 2019 ​ Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 Assets ​ ​ ​ ​ ​ ​ Money market funds(1) ​ $ 225,373 ​ $ — ​ $ — ​ $ 42,960 ​ $ — ​ $ — Asset-backed securities(2) ​ — ​ 24,250 ​ — ​ — ​ 20,000 ​ — Treasury bills(3) ​ ​ — ​ ​ 99,972 ​ ​ — ​ ​ — ​ ​ — ​ ​ — Corporate debt securities ​ ― ​ 27,919 ​ — ​ — ​ — ​ — Total assets ​ $ 225,373 ​ $ 152,141 ​ $ — ​ $ 42,960 ​ $ 20,000 ​ $ — Liabilities ​ ​ ​ ​ ​ ​ ​ ​ Convertible notes payable ​ $ — ​ $ 309,166 ​ $ — ​ $ — ​ $ 125,811 ​ $ — (1) Classified as cash and cash equivalents as of June 30, 2020 and December 31, 2019, respectively, on the consolidated balance sheets. (2) Includes $24,250 and $20,000 classified as cash and cash equivalents as of June 30, 2020 and December 31, 2019, respectively, on the consolidated balance sheets. (3) Includes $49,989 classified as cash and cash equivalents as of June 30, 2020 on the consolidated balance sheets.

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2020
Marketable Securities
Schedule of investments classified as available-for-sale	Marketable securities classified as available-for-sale as of June 30, 2020 and December 31, 2019 were comprised of (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2020 ​ December 31, 2019 ​ ​ ​ Gross Gross ​ ​ ​ ​ Gross Gross ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ ​ ​ ​ ​ Cost ​ Gains ​ Losses ​ Fair Value ​ Cost ​ Gains ​ Losses ​ Fair Value Treasury bills ​ $ 49,981 ​ $ 2 ​ $ — ​ $ 49,983 ​ $ — ​ $ — ​ $ — ​ $ — Corporate debt securities ​ $ 27,877 ​ $ 42 ​ $ — ​ $ 27,919 ​ $ — ​ $ — ​ $ — ​ $ — Total ​ $ 77,858 ​ $ 44 ​ $ — ​ $ 77,902 ​ $ — ​ $ — ​ $ — ​ $ —

Acquisition of Praha Vaccines_2

Acquisition of Praha Vaccines a.s. (Tables)	6 Months Ended
	Jun. 30, 2020
Acquisition of Praha Vaccines a.s.
Summary of preliminary allocation of the Purchase Price based upon the fair values of assets acquired and liabilities assumed at the Acquisition Date	The table below summarizes the preliminary allocation of the Purchase Price based upon the fair values of assets acquired and liabilities assumed at the Acquisition Date. The preliminary allocation is based upon information that was available to management at the time the consolidated financial statements were prepared and is subject to change prior to completion of the measurement period (in thousands): ​ ​ ​ ​ ​ Prepaid expense and other current assets $ 326 Property and equipment ​ 96,739 Goodwill ​ 70,468 Accounts payable ​ (1,193) Accrued expenses ​ (205) Other non-current liabilities ​ (813) Purchase Price, net of cash acquired ​ $ 165,322
Summary of unaudited pro forma financial information	The unaudited pro forma financial information for the periods set forth below gives effect to the Acquisition as if it had occurred as of January 1, 2019. The pro forma financial information is presented for informational purposes only and is not necessarily indicative of the results of operations that would have been achieved had the Acquisition been consummated as of that time. The unaudited pro forma financial information combines the historical results of operations of the Company and Praha Vaccines for the periods presented below and reflects the application of certain pro forma adjustments (in thousands, except per share amounts): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 ​ 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenue ​ $ 35,538 ​ $ 3,357 ​ $ 38,915 ​ $ 7,339 Net loss ​ (18,196) ​ (42,119) ​ (45,821) ​ (87,367) Basic and diluted net loss per share ​ (0.31) ​ (0.97) ​ (0.83) ​ (2.08)

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2020
Goodwill and Other Intangible Assets
Schedule of goodwill	The change in the carrying amounts of goodwill for the six months ended June 30, 2020 was as follows (in thousands): ​ ​ ​ ​ ​ ​ Amount Balance at December 31, 2019 ​ $ 51,154 Goodwill resulting from the acquisition of Praha Vaccines ​ ​ 70,468 Currency translation adjustments ​ (2,773) Balance at June 30, 2020 ​ $ 118,849
Schedule of identifiable intangible assets	Purchased intangible assets consisted of the following as of June 30, 2020 and December 31, 2019 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2020 ​ December 31, 2019 ​ Gross ​ ​ ​ ​ Gross ​ ​ ​ ​ ​ ​ Carrying ​ Accumulated ​ Intangible ​ Carrying ​ Accumulated ​ Intangible ​ ​ Amount ​ Amortization ​ Assets, Net ​ Amount ​ Amortization ​ Assets, Net Finite-lived intangible assets: ​ ​ ​ ​ ​ ​ Proprietary adjuvant technology ​ $ 7,991 ​ $ (2,764) ​ $ 5,227 ​ $ 7,985 ​ $ (2,562) ​ $ 5,423 Collaboration agreements ​ 3,608 ​ (3,585) ​ 23 ​ 3,606 ​ (3,448) ​ 158 Total identifiable intangible assets ​ $ 11,599 ​ $ (6,349) ​ $ 5,250 ​ $ 11,591 ​ $ (6,010) ​ $ 5,581
Schedule of estimated amortization expense	Estimated amortization expense for existing intangible assets for the remainder of 2020 and for each of the five succeeding years ending December 31 will be as follows (in thousands): ​ ​ ​ ​ ​ Year Amount 2020 (remainder) ​ $ 222 2021 ​ 400 2022 ​ 400 2023 ​ 400 2024 ​ 400 2025 ​ 400

Long-Term Debt (Tables)

Long-Term Debt (Tables)	6 Months Ended
	Jun. 30, 2020
Long-Term Debt
Schedule of convertible notes payable	Total convertible notes payable consisted of the following at (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, December 31, ​ ​ 2020 ​ 2019 Principal amount of the Notes ​ $ 325,000 ​ $ 325,000 Unamortized debt issuance costs ​ (3,677) ​ (4,389) Total convertible notes payable ​ $ 321,323 ​ $ 320,611
Schedule of interest expense	Interest expense incurred in connection with the Notes consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coupon interest at 3.75% ​ $ 3,047 ​ $ 3,047 ​ $ 6,094 ​ $ 6,094 Amortization of debt issuance costs ​ 356 ​ 356 ​ 712 ​ 712 Total interest expense on the Notes ​ $ 3,403 ​ $ 3,403 ​ $ 6,806 ​ $ 6,806

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2020
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Schedule of summary of option activity	The following is a summary of stock options and stock appreciation rights activity under the 2015 Plan and 2005 Plan for the six months ended June 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2015 Plan ​ 2005 Plan ​ ​ Weighted- ​ Weighted- ​ ​ ​ ​ Average ​ ​ ​ Average ​ ​ Stock Options ​ Exercise Price ​ Stock Options ​ Exercise Price Outstanding at January 1, 2020 3,388,701 ​ $ 35.64 501,780 ​ $ 64.19 Granted 2,820,041 ​ $ 22.28 — ​ $ — Exercised (209,959) ​ $ 30.35 (76,856) ​ $ 33.56 Canceled (32,254) ​ $ 41.18 (22,329) ​ $ 52.26 Outstanding at June 30, 2020 5,966,529 ​ $ 29.50 402,595 ​ $ 70.71 Shares exercisable at June 30, 2020 953,073 ​ $ 85.48 402,595 ​ $ 70.71 Shares available for grant at June 30, 2020 3,098,569 ​ ​
Schedule of assumptions used to estimate grant date fair value of stock options and stock appreciation rights granted using black-scholes option-pricing model	The ESPP is considered compensatory for financial reporting purposes. As such, the fair value of ESPP shares was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 Range of Black-Scholes fair value of ESPP shares granted ​ ​ $2.87-$21.80 ​ ​ $9.45-$34.78 ​ $2.57-$35.00 ​ ​ $7.25-$34.78 Risk-free interest rate ​ 1.5%-2.6% ​ ​ 1.3%-2.5% ​ ​ 1.5%-2.6% ​ ​ 1.2%-2.5% Dividend yield ​ 0% ​ 0% ​ 0% ​ 0% Volatility ​ 66.6%-150.9% ​ ​ 59.7%-171.6% ​ ​ 66.6%-154.4% ​ ​ 52.2%-171.6% Expected term (in years) ​ 0.5-2.0 ​ ​ 0.5-2.0 ​ ​ 0.5-2.0 ​ ​ 0.5-2.0 Expected forfeiture rate ​ 0% ​ 0% ​ 0% ​ 0%
Schedule of summary of restricted stock units activity	The following is a summary of restricted stock units activity for the six months ended June 30, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ Per Share ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ Number of ​ Grant-Date ​ ​ Shares ​ Fair Value Outstanding and Unvested at January 1, 2020 1,102,311 ​ $ 5.95 Restricted stock units granted 457,204 ​ $ 75.97 Restricted stock units vested (47,563) ​ $ 18.61 Restricted stock units forfeited (29,425) ​ $ 25.46 Outstanding and Unvested at June 30, 2020 1,482,527 ​ $ 26.75 ​
Schedule of stock-based compensation expense	The Company recorded all stock-based compensation expense in the consolidated statements of operations as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 Research and development ​ $ 4,098 ​ $ 2,444 ​ $ 6,005 ​ $ 5,624 General and administrative ​ 3,834 ​ 2,176 ​ 5,892 ​ 4,555 Total stock-based compensation expense ​ $ 7,932 ​ $ 4,620 ​ $ 11,897 ​ $ 10,179 ​
Stock options
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Schedule of assumptions used to estimate grant date fair value of stock options and stock appreciation rights granted using black-scholes option-pricing model	The fair value of stock options granted under the 2015 Plan was estimated at the date of grant or the date upon which the 2015 Plan was approved by the Company’s stockholders for stock options discussed above using the Black-Scholes option-pricing model with the following assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2020 2019 2020 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average Black-Scholes fair value of stock options granted ​ $77.41 ​ ​ $8.50 ​ $76.99 ​ ​ $23.43 ​ Risk-free interest rate ​ 0.3%-0.6% ​ ​ 1.8%-2.3% ​ ​ 0.3%-1.5% ​ ​ 1.8%-2.6% ​ Dividend yield ​ 0% ​ ​ 0% ​ ​ 0% ​ ​ 0% ​ Volatility ​ 116.0%-151.5% ​ ​ 127.3%-128.5% ​ ​ 116.0%-151.5% ​ ​ 111.6%-128.5% ​ Expected term (in years) ​ 3.9-7.6 ​ ​ 4.0 ​ 3.9-7.6 ​ ​ 4.0-4.5 ​ Expected forfeiture rate ​ 0% ​ ​ 0% ​ ​ 0% ​ ​ 0% ​

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended		58 Months Ended
	May 31, 2020	Sep. 30, 2015	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share				7,797,651	2,935,847
Restricted cash current			$ 106,768	$ 106,768		$ 106,768	$ 2,947
Purchase price held in escrow			11,200	11,200		11,200
Foreign currency translation adjustment			$ 13,200	$ 13,200		$ 13,200	$ 12,500
Series A Convertible Preferred Stock
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share				4,388,850
Preferred stock, shares outstanding			438,885	438,885		438,885
Catalent Maryland, Inc
Summary of Significant Accounting Policies [Line Items]
Purchase price held in escrow			$ 1,500	$ 1,500		$ 1,500
Bill Melinda Gates Foundation [Member]
Summary of Significant Accounting Policies [Line Items]
Grant Agreement		$ 89,100
Grant revenue recognized						82,000
Coalition for Epidemic Preparedness Innovations
Summary of Significant Accounting Policies [Line Items]
Restricted cash current			92,600	92,600		92,600
Initial Funding Development Costs	$ 384,500			388,400
Grant Funding
Summary of Significant Accounting Policies [Line Items]
Initial Funding Development Costs	245,900			245,900
Revenue recognized			34,200	36,500
Forgivable Loan Funding
Summary of Significant Accounting Policies [Line Items]
Initial Funding Development Costs	$ 142,500			142,500
Proceeds from funding agreement			76,000	$ 76,000		76,000
Convertible Debt Securities [Member]
Summary of Significant Accounting Policies [Line Items]
Number of shares excluded from the computation of net loss per share				2,385,800
Convertible Notes Initial Conversion Price Per Share				$ 136.20
Security Deposit [Member]
Summary of Significant Accounting Policies [Line Items]
Purchase price held in escrow			400	$ 400		400
Grant Agreement [Member]
Summary of Significant Accounting Policies [Line Items]
Restricted cash current			$ 1,400	$ 1,400		$ 1,400

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 424,395	$ 78,823
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	124,783	15,863
Money market funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	225,373	42,960
Asset-backed securities [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	24,250	$ 20,000
Treasury bills
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 49,989

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Reconciliation of cash, cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Cash and cash equivalents	$ 424,395	$ 78,823
Restricted cash current	106,768	2,947
Restricted cash non-current	411	410
Cash, cash equivalents and restricted cash	$ 531,574	$ 82,180	$ 78,235	$ 81,959

Fair Value Measurements - Fair

Fair Value Measurements - Fair value hierarchy for its financial assets and liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Level 1 [Member]
Assets
Total assets	$ 225,373	$ 42,960
Liabilities
Convertible notes payable	0	0
Level 1 [Member] | Money market funds [Member]
Assets
Total assets	225,373	42,960
Level 1 [Member] | Asset-backed securities [Member]
Assets
Total assets	0	0
Level 1 [Member] | Treasury bills
Assets
Total assets	0	0
Level 1 [Member] | Corporate debt securities [Member]
Assets
Total assets	0	0
Level 2 [Member]
Assets
Total assets	152,141	20,000
Liabilities
Convertible notes payable	309,166	125,811
Level 2 [Member] | Money market funds [Member]
Assets
Total assets	0	0
Level 2 [Member] | Asset-backed securities [Member]
Assets
Total assets	24,250	20,000
Level 2 [Member] | Treasury bills
Assets
Total assets	99,972	0
Level 2 [Member] | Corporate debt securities [Member]
Assets
Total assets	27,919	0
Level 3 [Member]
Assets
Total assets	0	0
Liabilities
Convertible notes payable	0	0
Level 3 [Member] | Money market funds [Member]
Assets
Total assets	0	0
Level 3 [Member] | Asset-backed securities [Member]
Assets
Total assets	0	0
Level 3 [Member] | Treasury bills
Assets
Total assets	0	0
Level 3 [Member] | Corporate debt securities [Member]
Assets
Total assets	$ 0	$ 0

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 424,395	$ 78,823
Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value	24,250	$ 20,000
Treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 49,989

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 77,858	$ 0
Gross Unrealized Gains	44	0
Gross Unrealized Losses	0
Fair Value	77,902
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,877	0
Gross Unrealized Gains	42	0
Gross Unrealized Losses	0
Fair Value	27,919
Treasury bills
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	49,981	0
Gross Unrealized Gains	2	$ 0
Gross Unrealized Losses	0
Fair Value	$ 49,983

Acquisition of Praha Vaccines_3

Acquisition of Praha Vaccines a.s. (Details) - May 27, 2020 - Praha Vaccines a.s € in Millions, $ in Millions	EUR (€)	USD ($)	USD ($)
Business Acquisition [Line Items]
Total consideration	€ 151.7	$ 167.3
Purchase Price placed in an escrow account	€ 10		$ 11.1

Acquisition of Praha Vaccines_4

Acquisition of Praha Vaccines a.s. - Preliminary allocation of the Purchase Price (Details) - USD ($) $ in Thousands	May 27, 2020	Jun. 30, 2020	Dec. 31, 2019
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Goodwill		$ 118,849	$ 51,154
Praha Vaccines a.s
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Prepaid expense and other current assets	$ 326
Property and equipment	96,739
Goodwill	70,468
Accounts payable	(1,193)
Accrued expenses	(205)
Other non-current liabilities	(813)
Purchase Price, net of cash acquired	$ 165,322
Minimum | Praha Vaccines a.s
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Expected remaining useful lives of fixed assets	4 years
Maximum | Praha Vaccines a.s
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]
Expected remaining useful lives of fixed assets	25 years

Acquisition of Praha Vaccines_5

Acquisition of Praha Vaccines a.s. - The unaudited pro forma financial information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Business Acquisition [Line Items]
Net income from the acquisition date through June 30, 2020	$ 1,800
Revenue		$ 35,538	$ 3,357	$ 38,915	$ 7,339
Net loss		$ (18,196)	$ (42,119)	$ (45,821)	$ (87,367)
Basic and diluted net loss per share		$ (0.31)	$ (0.97)	$ (0.83)	$ (2.08)
General and administrative [Member]
Business Acquisition [Line Items]
Costs related to the acquisition		$ 1,900

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Schedule of Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020USD ($)
Goodwill and Other Intangible Assets
Beginning balance	$ 51,154
Goodwill resulting from the acquisition of Praha Vaccines	70,468
Currency translation adjustments	(2,773)
Ending balance	$ 118,849

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Schedule of Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 11,599	$ 11,591
Accumulated Amortization	(6,349)	(6,010)
Intangible Assets, Net	5,250	5,581
Proprietary adjuvant technology
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	7,991	7,985
Accumulated Amortization	(2,764)	(2,562)
Intangible Assets, Net	5,227	5,423
Collaboration agreements
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,608	3,606
Accumulated Amortization	(3,585)	(3,448)
Intangible Assets, Net	$ 23	$ 158

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Schedule of Estimated Amortization Expense (Details) $ in Thousands	Jun. 30, 2020USD ($)
Goodwill and Other Intangible Assets
2020 (remainder)	$ 222
2021	400
2022	400
2023	400
2024	400
2025	$ 400

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Goodwill and Other Intangible Assets
Amortization of Intangible Assets	$ 0.3	$ 0.3

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Jun. 30, 2020	Dec. 31, 2019
Long-Term Debt
Debt Issuance Costs	$ 10,000
Aggregate principal amount of notes issued		$ 325,000	$ 325,000
Debt issuance cost amortization period	7 years

Long-Term Debt - Notes Payable

Long-Term Debt - Notes Payable (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Long-Term Debt
Principal amount of Notes	$ 325,000	$ 325,000
Unamortized debt issuance costs	(3,677)	(4,389)
Total convertible notes payable	$ 321,323	$ 320,611

Long-Term Debt - Interest Expen

Long-Term Debt - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Long-Term Debt
Coupon interest at 3.75%	$ 3,047	$ 3,047	$ 6,094	$ 6,094
Amortization of debt issuance costs	356	356	712	712
Total interest expense on Notes	$ 3,403	$ 3,403	$ 6,806	$ 6,806
Coupon interest rate	3.75%	3.75%	3.75%	3.75%

Preferred Stock (Details)

Preferred Stock (Details) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)$ / sharesshares
Class of Stock [Line Items]
Number of shares into with each preferred share is converted | shares	10
Conversion price	$ 45.57
Beneficial conversion feature | $	$ 24.1
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Shares sold | shares	438,885
Par value per share	$ 0.01
Purchase price	$ 455.70
Proceeds from issuance of convertible stock | $	$ 200

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2017	May 31, 2020	Jan. 31, 2020	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Gross proceeds						$ 393,763	$ 55,242
Proceeds from shares sold		$ 207,845		$ 3		$ 393,763	$ 55,242
David M. Mott
Subsidiary, Sale of Stock [Line Items]
Shares sold	32,916
Purchase price	$ 45.57	$ 45.57				$ 45.57
Gross proceeds	$ 1,500
December 2018 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Shares sold			7,200,000		1,700,000
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value											$ 100,000
Proceeds from shares sold			$ 38,500		$ 17,400
December 2017 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Shares sold					2,500,000
Proceeds from shares sold					$ 37,900			$ 75,000
January 2020 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Shares sold			10,500,000
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value										$ 100,000
Proceeds from shares sold			$ 98,700
March 2020 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Shares sold						8,600,000
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value			$ 150,000
Proceeds from shares sold						$ 148,100
May 2020 Sales Agreement [Member]
Subsidiary, Sale of Stock [Line Items]
Shares sold						2,200,000
Shelf Registration Statement, Maximum Authorized Common Stock Issuance, Value									$ 250,000
Proceeds from shares sold						$ 107,000
Remaining amount under the agreement	141,600,000	141,600,000				141,600,000

Stock-Based Compensation (Detai

Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended	12 Months Ended
	Apr. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of stock options and stock appreciation rights exercised		$ 7.8	$ 0.1
Unrecognized compensation expense		$ 344		$ 344
Unrecognized compensation expense, recognition period				1 year 6 months
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted				457,204
2005 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of options and stock appreciation rights				10 years
Minimum grant price, percent of common stock fair value		100.00%		100.00%
Aggregate intrinsic value of stock options and stock appreciation rights outstanding		$ 357.5		$ 357.5
Weighted-average remaining contractual term of stock options and stock appreciation rights outstanding				8 years 6 months
Aggregate intrinsic value of stock options and stock appreciation rights exercisable		$ 34.1		$ 34.1
Weighted-average remaining contractual term of stock options and stock appreciation rights exercisable				5 years 3 months 18 days
2005 Plan [Member] | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				4 years
2005 Plan [Member] | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period				1 year
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		10,900,000		10,900,000
Increase in issuance of common stock				7,100,000
Shares available for grant		3,098,569		3,098,569
Aggregate intrinsic value of stock options and stock appreciation rights outstanding		$ 357.5		$ 357.5
Weighted-average remaining contractual term of stock options and stock appreciation rights outstanding				8 years 6 months
Aggregate intrinsic value of stock options and stock appreciation rights exercisable		$ 34.1		$ 34.1
Weighted-average remaining contractual term of stock options and stock appreciation rights exercisable				5 years 3 months 18 days
Granted				2,820,041
Weighted-average exercise price				$ 22.28
Expected Volatility Rate		151.50%
2015 Plan [Member] | Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted					192,400
Weighted-average exercise price					$ 5.95
2015 Plan [Member] | Stock options | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	2,501,600
Weighted-average exercise price	$ 19.08
2015 Plan [Member] | Restricted stock units | Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted	326,050
2015 Plan [Member] | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted					1,014,200
Weighted-average exercise price					$ 5.95
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		600,000		600,000
Shares available for grant		278,543		278,543
Maximum compensation allowed to utilize for plan		15.00%		15.00%
Maximum discount rate from market price				85.00%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Option Activity (Details)	6 Months Ended
	Jun. 30, 2020$ / sharesshares
2005 Plan [Member]
Stock Options
Outstanding at January 1, 2020	501,780
Exercised	(76,856)
Canceled	(22,329)
Outstanding at June 30, 2020	402,595
Shares exercisable at June 30, 2020	402,595
Weighted-Average Exercise Price
Outstanding at January 1, 2020 | $ / shares	$ 64.19
Exercised | $ / shares	33.56
Canceled | $ / shares	52.26
Outstanding at June 30, 2020 | $ / shares	70.71
Shares exercisable at June 30, 2020 | $ / shares	$ 70.71
2015 Plan [Member]
Stock Options
Outstanding at January 1, 2020	3,388,701
Granted	2,820,041
Exercised	(209,959)
Canceled	(32,254)
Outstanding at June 30, 2020	5,966,529
Shares exercisable at June 30, 2020	953,073
Shares available for grant at June 30, 2020	3,098,569
Weighted-Average Exercise Price
Outstanding at January 1, 2020 | $ / shares	$ 35.64
Granted | $ / shares	22.28
Exercised | $ / shares	30.35
Canceled | $ / shares	41.18
Outstanding at June 30, 2020 | $ / shares	29.50
Shares exercisable at June 30, 2020 | $ / shares	$ 85.48

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions Used in Estimation of Fair Value of Stock (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility, maximum				128.50%
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	1.50%	1.30%	1.50%	1.20%
Risk-free interest rate, maximum	2.60%	2.50%	2.60%	2.50%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility, minimum	66.60%	59.70%	66.60%	52.20%
Volatility, maximum	150.90%	171.60%	154.40%	171.60%
Expected forfeiture rate	0.00%	0.00%	0.00%	0.00%
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average Black-Scholes fair value of stock options and SARs granted	$ 77.41	$ 8.50	$ 76.99	$ 23.43
Risk-free interest rate, minimum	0.30%	1.80%	0.30%	1.80%
Risk-free interest rate, maximum	0.60%	2.30%	1.50%	2.60%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility	151.50%
Volatility, minimum	116.00%	127.30%	116.00%	111.60%
Volatility, maximum		128.50%	151.50%
Expected term (in years)		4 years
Expected forfeiture rate	0.00%	0.00%	0.00%	0.00%
Minimum | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average Black-Scholes fair value of stock options and SARs granted	$ 2.87	$ 9.45	$ 2.57	$ 7.25
Expected term (in years)	6 months	6 months	6 months	6 months
Minimum | 2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	3 years 10 months 24 days		3 years 10 months 24 days	4 years
Maximum | Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average Black-Scholes fair value of stock options and SARs granted	$ 21.80	$ 34.78	$ 35	$ 34.78
Expected term (in years)	2 years	2 years	2 years	2 years
Maximum | 2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	7 years 7 months 6 days		7 years 7 months 6 days	4 years 6 months

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Restricted Stock Awards Activity (Details) - Restricted stock units	6 Months Ended
	Jun. 30, 2020$ / sharesshares
Number of shares
Outstanding and Unvested at January 1, 2020 | shares	1,102,311
Restricted stock units granted | shares	457,204
Restricted stock units vested | shares	(47,563)
Restricted stock units forfeited | shares	(29,425)
Outstanding and Unvested at June 30, 2020 | shares	1,482,527
Per Share Weighted-Average Grant-Date Fair Value
Outstanding and Unvested at January 1, 2020 | $ / shares	$ 5.95
Restricted stock units granted | $ / shares	75.97
Restricted stock units vested | $ / shares	18.61
Restricted stock units forfeited | $ / shares	25.46
Outstanding and Unvested at June 30, 2020 | $ / shares	$ 26.75

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 7,932	$ 4,620	$ 11,897	$ 10,179
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	4,098	2,444	6,005	5,624
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 3,834	$ 2,176	$ 5,892	$ 4,555

U.S. Government Agreements, G_2

U.S. Government Agreements, Grants and Licenses - Operation Warp Speed (Details) - Operation Warp Speed - Project Agreement $ in Millions	1 Months Ended
	Jun. 30, 2020USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial funding	$ 1,600
Authorized expenditures or obligations	$ 800
Doses of the vaccine candidate	100

U.S. Government Agreements, G_3

U.S. Government Agreements, Grants and Licenses - U.S. Department of Defense (Details) - U.S. Department of Defense - DoD Contract $ in Millions	1 Months Ended	3 Months Ended
	Jun. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Jun. 30, 2020USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial funding	$ 60
Authorized expenditures or obligations	$ 22
Most-favored customer status period	5 years
Revenue recognized			$ 0.3
Forecast
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Doses of the vaccine candidate		10

U.S. Government Agreements, G_4

U.S. Government Agreements, Grants and Licenses - Coalition for Epidemic Preparedness Innovations (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	6 Months Ended
	May 31, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2020
Coalition for Epidemic Preparedness Innovations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial funding development costs	$ 384.5			$ 388.4
Additional funding development cost		$ 3.9
Grant Funding
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial funding development costs	245.9			245.9
Revenue recognized			$ 34.2	36.5
Forgivable Loan Funding
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial funding development costs	$ 142.5			$ 142.5

U.S. Government Agreements, G_5

U.S. Government Agreements, Grants and Licenses - Bill & Melinda Gates Foundation (Details) $ in Thousands, item in Millions	Sep. 15, 2015	May 31, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2015USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)item	Jun. 30, 2019USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contracts Revenue					$ 35,538	$ 3,357	$ 38,915	$ 7,339
Bill Melinda Gates Foundation [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contracts Revenue					$ 200		400
Grant Agreement				$ 89,100
Global Access Commitments Agreement GACA [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract term after first sale	15 years
Contract term	10 years
Contract term additional years	5 years
Coalition for Epidemic Preparedness Innovations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial Funding Development Costs		$ 384,500					$ 388,400
Additional Funding Development Cost			$ 3,900
Takeda Pharmaceutical Company Limited | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of manufacturing capacity doses | item							250