Viruses evolve to be more fit. Presumably, a mild version and more contagious version may even have evolved in one of the billions that were infected these year

Viruses evolve to be more fit. Presumably, a mild version and more contagious version may even have evolved in one of the billions that were infected these years, but it didn't spread much because of self-isolation and restrictions. A variand that s more debilitating would be less likely to transmit.