Stock option plans (Tables)

12 Months Ended

Dec. 31, 2021

Stock option plan

Schedule of assumptions used in valuation of stock options

	Year ended December 31,
	2021	2020	2019
Expected volatility	88.1% ‑90.2%	78.9% ‑83.8%	73.5% ‑74.5%
Risk‑free rate	0.96% ‑1.04%	0.36% ‑1.43%	1.53% ‑2.63%
Expected dividend yield	0%	0%	0%
Expected term in years	5.50-6.08	5.50-6.08	6.08-7.59

Summary of stock option activity

			Weighted‑		Weighted
			average		average
			exercise		remaining	Aggregate
	Number of		price per		contractual	intrinsic
	options		share		term (in years)	value
Outstanding at January 1, 2019		1,844,188	$	0.82	7.6
Granted		2,018,796		8.82
Exercised		(322,267)		0.23
Cancelled/Forfeited		(40,783)		0.99
Outstanding at December 31, 2019		3,499,934	$	5.49	7.5
Granted		446,800		35.51
Exercised		(164,075)		0.92
Cancelled/Forfeited		(11,200)		38.78
Outstanding at December 31, 2020		3,771,459	$	9.10	6.8
Granted		1,179,650		5.87
Exercised		(226,394)		0.92
Cancelled/Forfeited		(138,100)		16.53
Outstanding at December 31, 2021		4,586,615	$	8.45	6.6	$	2,101,398
Exercisable at December 31, 2021		2,518,554	$	6.89	5.5	$	2,093,937
Vested or expected to vest at December 31, 2021		4,586,615	$	8.45	6.6	$	2,101,398

Summary of restricted stock units activity

		Weighted‑
		average
		grant date
	Shares	fair value
Restricted stock units outstanding at December 31, 2020	—	$	—
Granted	523,050		5.91
Vested	(107,331)		5.94
Cancelled/Forfeited	(16,000)		6.00
Outstanding at December 31, 2021	399,719	$	5.91