You realise that you have never needed that yellow book to keep your job, get healthcare, or enter a shopping mall or restaurant (which seems to be the direction that this is heading)? You might also appreciate that accessing the information on a piece of card cannot be digitally logged and tracked, and neither can the information it contains be arbitrarily changed or suspended.You realise that there is already a vaccine passport. It's a yellow book you get that you show in a foreign country at arrivals.
This is just the digital version. Saves me having to dig that yellow book out to prove I have had yellow fever/typhoid vaccines for instance.