There is a lot of suspect "information" out there, some of which probably is correct, but most of it is speculative and salted with words like "could" and "might" and "possible". It may take some time to develop an accurate depiction of what transpired. I'm not going to cherry pick reports that comport with what I would like to be the case.
I'm a bit surprised - and perhaps it has been done - no one has offered a fairly broad scale report of AB testing to see how widely this has spread using a representative sample of the population. I've seen some local studies here and there, and I've heard anecdotal reports that a person was sick back in November, but I can't make much of that.