Bacteriology was already developing at that time, first vaccines were already in use (for none other than a viral disease!), and the existence of a pathogen smaller than bacteria was already hypothesized. The response to Spanish flu was also eerily similar to what was recommended in the first year of COVID: https://en.m.wikipedia.org/wiki/Spanish_flu#/media/File%3AIl....
All that aside, your comment does not really prove that "nature cannot come up with something so transmissive", which was the claim here.
All that aside, your comment does not really prove that "nature cannot come up with something so transmissive", which was the claim here.