that could be a confounding factor, but it's hard to know for sure without really digging into their data and methods. they may have tried to correct for that.

that could be a confounding factor, but it's hard to know for sure without really digging into their data and methods. they may have tried to correct for that. in any case, this study actually seems to suggest that while vaccination probably has a marginal benefit, the effect size is too small to really matter.