Nature of Business - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended						9 Months Ended
	Jul. 31, 2021	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) geneticMutation product dose segment orphan_drug_designation	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments | segment								1
Number of vaccination dose regimen | dose								2
Vaccination dose regimen, duration apart								28 days
Overall vaccine efficacy (percentage)	77.80%
Efficacy, severe cases (percentage)	93.40%
Efficacy, asymptomatic infection (percentage)	63.60%
Adverse events, side effects (percentage)	12.40%
Adverse events, serious adverse side effects (less than) (percentage)	0.50%
Efficacy against delta variant, B.1.617.2 (percentage)	65.20%
Single gene replacement therapies, number of genetic mutations target | geneticMutation								1
Modifier gene therapy platform, number of products | product								1
Number of ODDs received (orphan drug designation) | orphan_drug_designation								4
Net loss		$ 10,755	$ 25,952	$ 7,077	$ 10,474	$ 3,614	$ 3,944	$ 43,784	$ 18,032
Accumulated deficit		117,086						117,086		$ 73,302
Cash, cash equivalents and restricted cash		$ 107,500			$ 19,257			$ 107,500	$ 19,257	$ 24,190	$ 7,595