[inflagranti]

At least in the UK the vaccine passports are made available through the NHS App, and stored AFAIK the same way any other health information on your person is stored already. At least they show up the same way like all other healthcare appointments, prescription s, etc. The only unique things are the QR codes to "export" that information - the validity of this is not checked against a (separate) database to my knowledge.

Other countries that have nationwide systems should have been able to do something similar - of course there's a good chance they didn't, but that's really not an argument against Covid passports but against bad security practices.