> It would be odd if our immune system, as had apparently been speculated, became less effective against pathogens that it saw a lot. That actually can happen.

> It would be odd if our immune system, as had apparently been speculated, became less effective against pathogens that it saw a lot. That actually can happen. It's called "original antigenic sin" or "immunological imprinting". https://en.m.wikipedia.org/wiki/Original_antigenic_sin https://en.m.wikipedia.org/wiki/Original_antigenic_sin It's especially prevalent in respiratory viruses. The flu is a well known case. The more flu shots you have (the yearly one), the less effective they become (while still more effective than nor having one).