That is the USUAL case.
I hope it’s still true here.
It’s as if viruses play a balancing act. If they infect easily, that is enough for them to survive and the fatality rate isn’t high.
But if they can’t infect easily, they tend to be very powerful and deadly. They’re making up for their deficiency that way.
E.g, in honesty COVID has no more than 1% death rate. Its cousins, like MERS and SARS, have something like 30% and 11% death.
Viruses that kill their hosts don’t survive. So it is a form of viral Darwinism to mutate into less fatal, less severe forms.
Correct: viruses tend to become less virulent over time.