That's how you know it's not just a public health measure. For other vaccines, we rely on the majority being vaccinated so that any isolated outbreaks are naturally contained. I assume google doesn't ask you to prove you're vaccinated against measles for example. If one person is not vaccinated, it's to their detriment and irrelevant to everyone else. There are weak arguments about vaccine efficacy etc that some people could still get infected, but the point is that majority voluntary vaccination contains disease to the point that there is no justification of invasive personal measures (in this case disclosing personal health information to an information predator, but its unacceptable regardless of the employer). It seems to me this is much more about signaling to their various stakeholders about their politics rather than an actual public health campaign.

FWIW I think (I think) they should be allowed to enforce this if they want, even if i dont like it. Although I might support measures to make this kind of discrimination illegal, I'd have to think more about that. Despite having my vaccine, I would not work for a company that asked me to prove it, however. I've got no beef with the vaccine, only with giving state or corporate actors power over my health choices.