" A dead host cannot easily spread the germ to others, so causing milder illness is “better” for the pathogen from a Darwinian point of view. People who are very sick stay home in bed or die, and those who are only mildly sick continue with their lives, preferentially spreading milder strains of the pathogen. "

― Nicholas A. Christakis , Apollo's Arrow: The Profound and Enduring Impact of Coronavirus on the Way We Live