AFAIK viruses tend to mutate to be less lethal because killing the host is bad for reproduction.
random source: https://en.wikipedia.org/wiki/Spanish_flu
>This is a common occurrence with influenza viruses: there is a tendency for pathogenic viruses to become less lethal with time, as the hosts of more dangerous strains tend to die out
The ideal evolutionary strategy is to produce excess bodily fluids from sweating, coughing and sneezing, while not making people so sick that they lay down and stay home, let alone die.
Viruses don’t get bonus points for being lethal, unlike certain video games.