In a prior probability sense, that makes sense, right? The adaptive immune system has to be working or the vaccines wouldn't work, and adapting against the actual threat has to be effective or you'd never have fought it off in the first place.

Of course, the general problem here is one of measurability and working in an adverse environment. So in a medical sense, prior infection determines response. But in a public health sense, if you believe that prior infection claims are easier to fake than vaccine records, and if you believe the spread risk is worse, then it makes sense to proxy spread risk with vaccine records. Personally, I get what you mean, and perhaps I'm not fighting too hard for the truth here because I don't really care that much.

But I just wanted to say I'm with you on the facts since every other response is operating (in my opinion) in the fallacious "there's a paper that says" mode. It's just not Bayesian.