I'm genuinely asking, I'm a simple software dev not a doctor.
FWIW, I was trained as a bacterial geneticist and routinely used bacteriophage (viruses that infect bacteria) with various resistance mutations.
Viral mutations are not restricted to viruses that infect bacteria.
edit: in fact, fundamental aspects of the genetic code were determined by analyzing and exploiting viral mutations.
https://en.wikipedia.org/wiki/Crick,_Brenner_et_al._experime...
The Crick, Brenner et al. paper that I cited above
* studied mutations in a viral gene called "rIIB"
* the authors used those rIIB mutations to determine that the genetic code was a non-overlapping triplet (now called codons) -- a pretty fundamental discovery.
* What's amazing to me is that they still have NO IDEA what the rIIB gene actually _does_, mechanistically.
It's like learning a little bit about God using an enigma machine (sorry, shitty simile).