[cabmandone]

Originally Posted by javadog

Start with the fact that the two viruses are completely different.

A little relevant info here:

https://www.google.com/amp/s/www.news-medical.net/amp/health/Smallpox-Evolution.aspx

They're different in how they replicate. That doesn't explain why pressuring one vs the other won't result in mutations with one but not the other.