> not quite as much evolutionary pressure if the virus spreads during its presymptomatic period That isn’t the only form of evolutionary pressure. The more you

> not quite as much evolutionary pressure if the virus spreads during its presymptomatic period That isn’t the only form of evolutionary pressure. The more your host population builds up immunity to the viral bag of tricks the more evolutionary trade offs there must be to remain infectious and over time they tend to harm the virulence. For example, Omicron seems to be very good at replicating in the upper respiratory but not so good in the lungs. Destructive mutations can still occur but they become much less probable over time. > Omicron mutated a whole lot without spreading One theory is that it did mutate through spread but in mice not humans. [1] 1: https://www.biorxiv.org/content/10.1101/2021.12.14.472632v1.full.pdf https://www.biorxiv.org/content/10.1101/2021.12.14.472632v1....