Is it possible that the vaccines aren't as good as we think due to sampling bias? I've had this thought running around my head for a while. The vaccines all look very good; the ones that aren't don't seem to be making the cut (Merck). 

But we're presumably seeing a very biased sample here - those that are in the trial presumably would be more vigilant about wearing masks and social distancing than the general population; additionally, with mask requirements in many stores and many still on some form of stay-at-home requirements, the R-naught is low enough that we're not seeing the true efficacy of the vaccines. 

&amp;#x200B;

Is that plausible, or do the sample sizes and statistical analysis account for that?