Stockholder's equity (deficit) - Common stock (Details)						3 Months Ended	6 Months Ended
	Jun. 17, 2022 USD ($)	Jun. 15, 2022 $ / shares shares	May 18, 2021 USD ($) shares	Jul. 10, 2020 USD ($) $ / shares shares	Jun. 24, 2019 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) Vote $ / shares shares	Dec. 31, 2021 $ / shares shares	Jun. 18, 2019 shares
Class of Stock [Line Items]
Common stock, shares authorized						150,000,000	150,000,000	150,000,000
Common stock, par value (in dollars per share) | $ / shares						$ 0.0001	$ 0.0001	$ 0.0001
Number of votes per share | Vote							1
Cash dividend declared | $ / shares							$ 0
Cash dividend paid | $ / shares							$ 0
Proceeds received, net of underwriting discounts and commissions | $							$ 25,000,000
Share Issued value under agreement | $						$ 24,647,000
Common stock, shares issued						37,570,326	37,570,326	34,900,727
Common stock, shares outstanding						37,570,326	37,570,326	34,900,727
Common stock were reserved for issuance
Options available for future grant						14,767,109	14,767,109	12,982,822
Options available for future grant
Common stock were reserved for issuance
Options available for future grant						2,612,856	2,612,856	1,889,299
Common stock Available under ATM Offering
Class of Stock [Line Items]
Proceeds received, net of underwriting discounts and commissions | $	$ 24,647,000
Offering costs | $	$ 353,000
Sale of stock under agreement						0
Common stock were reserved for issuance
Options available for future grant			5,000,000			5,000,000	5,000,000	5,000,000
Common stock Available under ATM Offering | Pfizer Inc
Class of Stock [Line Items]
Sale of stock under agreement		2,525,252
Sale of stock, price per share | $ / shares		$ 9.90
Warrants to Purchase Common Stock
Common stock were reserved for issuance
Options available for future grant						36,718	36,718
Warrants Available for Future Grant
Common stock were reserved for issuance
Options available for future grant						146,880	146,880
2018 Stock option and grant plan
Common stock were reserved for issuance
Options available for future grant						1,889,683	1,889,683	2,011,891	107,635
2019 Stock Option and Incentive plan
Common stock were reserved for issuance
Options available for future grant						3,881,675	3,881,675	3,209,203
2019 Employee Stock Purchase Plan
Common stock were reserved for issuance
Options available for future grant						1,199,297	1,199,297	872,429
Maximum | Common stock Available under ATM Offering
Class of Stock [Line Items]
Share Issued value under agreement | $			$ 100,000
IPO
Class of Stock [Line Items]
Public offering price | $ / shares					$ 16.00
Proceeds received, net of underwriting discounts and commissions | $					$ 98,394,000
Offering costs | $					$ 2,942,000
Number of shares converted					21,056,136
Common stock, shares issued					6,612,500
Follow Up Public Offering
Class of Stock [Line Items]
Share Issued under agreement				6,012,390
Public offering price | $ / shares				$ 36.00
Proceeds received, net of underwriting discounts and commissions | $				$ 203,460,000
Offering costs | $				$ 906,000
Over allotment | Maximum
Class of Stock [Line Items]
Share Issued under agreement				784,224
Common stock, shares issued					862,500