you dont need a database.
you can instead just have smart contracts
imagine a vaccine centre signs with their keypair a message of
patient ID: <your personal publickey>
date: 12/3/21
batch: 143
that signature is proof you got vaccinated by that vaccine centre.
each signature is unique but each signature has a validation method.
you can carry around that signature and that signature can verify its contents. with a simple check
you can prove you are that patient by you signing your own message that corresponds to your public key
no database. no blocks no chains needed
airlines dont need access to all patient records. dont even need to validate all records on some database
they just ask for the signature from those wanting to fly
I think this is a really good solution. It's low cost, secure, and can be used internationally. I would include the type of vaccine (eg, Sinovac, Pfizer, etc) because it might turn out that some of them do not work. Also one would need to keep each message, for the first vaccine, second vaccine, booster shot, etc, and the business could look at all of this information to determine if a person is 10 days out from the 2nd vaccine (if it is a 2-vaccine series).