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