On covid reinfection, a virologist's take :
"... And covid is barely mutating the parts that the immune system recognizes (the spike protein), so once a patient beats their high level of virus, they would easily be able to beat back whatever little virus they might get exposed to from others.
That’s how immunity works. Immunity can fade, but not on the scale on weeks that these reports suggest. Maybe after a year. So for now, these reports of “reinfections” are likely just an artifact of imperfect testing."