Yes for this to work you are going to have to screen a lot of people with mild cases to find the very rare mutant that is attenuated. The chance this rare mutat

Yes for this to work you are going to have to screen a lot of people with mild cases to find the very rare mutant that is attenuated. The chance this rare mutating just happens to infect an immune compromised person is low. Just looking through the entire population of mild cases will be much quicker as the limiting factor is not the genome sequencing of the viral strains.