Yeah, this is selecting for people participating in a medical study, it is far from a random sampling. Lots of very rural America would be ruled out, even if t

Yeah, this is selecting for people participating in a medical study, it is far from a random sampling. Lots of very rural America would be ruled out, even if the study participants weren't all from traditional big cities. People that are less mobile also wouldn't participate, etc. Lots of people who wouldn't contract COVID early would also not be likely to participate in this kind of trial. Plus the positives in this case weren't all in January, they spread into March (by which point in time finding positives becomes much more likely). And that's aside from the difficulties with antibody testing and cross-reactivity -- although this study looks a lot better than the previous one.