Out, about, and willing to speak to a stranger, which I think is the biggest bias. Pretty much everyone I know goes on the occasional walk, but we all stay the fuck away from other people.
Change in Human Social Behavior in Response to a Common Vaccine
https://pubmed.ncbi.nlm.nih.gov/20816312/
Conclusions: These results show that there is an immediate active behavioral response to infection before the expected onset of symptoms or sickness behavior.