Experience.

A good friend has a daughter in college at Penn State. She is 18 and a high school athlete who was in top condition. She contracted Covid and now tests negative but has experienced tons of continuing health problems, including severe fatigue, shortness of breath (can’t even jog now), strange issues with sense of smell, etc.

For people paying attention, covid should be a real concern and the idea of pursuing herd immunity as a national strategy is very misguided.