As more countries look to adopt digital COVID-19 vaccine passports, one American tech expert says the certificates should be developed using a “privacy-preserving approach.”

“There’s a lot of us who have deep concerns about issues of equity, issues of, obviously, privacy … if you were to implement the [vaccine passport] system,” said Brian Behlendorf, managing director of blockchain, health care and identity at the Linux Foundation, a non-profit that is working on vaccine passport software.