NY runs its Vaccine passport on an IBM blockchain citing privacy benefits:

>special emphasis has been placed on the protection of an individual's privacy. Secure technologies, like blockchain and encryption, are woven throughout Excelsior Pass to help protect the data, making it verifiable and trusted. No private health data is stored or tracked within the apps. Excelsior Pass can be used to voluntarily show a QR code as proof of COVID-19 vaccination or negative test result via a digital smartphone wallet or printed credential without sharing underlying personal health details.

https://www.governor.ny.gov/news/governor-cuomo-announces-la...