So I guess we can just choose which study to believe.

Only if you are looking to reinforce your beliefs. Otherwise, besides the above two strategies, you should look at which study has better methodology (though it's usually never trivial, especially not for us, bystanders), bigger sample size, stronger statistical power.

If none of these seem to suggest a clear winner then you should just think that this is still undecided. You can also ask an expert. Choosing one and believing is basically just going with your suspicion.

Rules of thumb:

a) choose the later study

b) look at what happens in the real world (e.g. https://news.ycombinator.com/item?id=29124652 )

And, If there is uncertainty (and there always is some small amount of it) then this does not support the parent commenter's strong and confident assertion that "do not, and never have" ... produced an effect.

a) we are in a small enough time frame that the latest doesn't mean it is more accurate

b) in the real world, we had our biggest outbreak after vaccines were mainstream

> in the real world, we had our biggest outbreak after vaccines were mainstream

Is that supposed to be relevant? When "we had our biggest outbreak" there were/are still sufficient unvaccinated people to transmit an outbreak.

You're clearly defending a fixed point of view here. If you want detailed responses to learn from, stop asking for people to do them yet again and look for what already exists upthread. If you're having trouble finding it, start here: https://news.ycombinator.com/item?id=29124446