system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't other viruses nearly eradicated by vaccines not evolve to evade immunity like Covid does?

Covid-19 has seen lots of variants that evade the immune response from prior variants, either acquired from the virus or from vaccines made based on their spike protein characteristics.

Measles is incredibly infectious but historically we were able to nearly eliminate it in the Western world. Why did it not evolve to evade vaccine induced immunity like Covid does?
gpt
Flu is able to swap large sections of its genome, since it is segmented.  It also travels through various different species (birds, pigs, human etc), so flu can and does mutate quite a bit.  More than CoVid, by far.  CoVid and measles mutate at the same rate on a molecular level, but the measles spike protein is very highly constrained, and any number of mutations that would allow it to escape neutralizing antibodies would inactivate its ability to bind and enter the cell. Unfortunately we are learning that CoVid is not nearly as constrained, and is able to remain effective at binding even in light of multiple mutations.