[pndy]

QR code can be spoofed and that happened already - there were certificates issued for e.g. Adolf Hitler and also for Mickey Mouse with govt health agency signature [1]; these were using French and German keys. Both are invalidated of course. And not mention all "classic" written physical information cards - these are around too for people who want to avoid vaccines for whatever reasons they want.

[1] - https://niebezpiecznik.pl/post/falszowanie-certyfikat-covid-... (in Polish)

On a paper this looks great - hell, the solution might even work for a time but additional unexpected factors may spawn out of nowhere and destroy whole thing.