There is some research that there is an immune boost to regular public transit riders. Evidence points to regular riders getting less sick than occasional riders, and that can extrapolate to occasional public interaction.

> Seasoned public transportation commuters, though, seem to be better protected against the viruses. “These data are very plausible when we think about the greater likelihood of developing protective antibodies to common respiratory viruses if repeatedly exposed,”

https://www.webmd.com/cold-and-flu/news/20110120/catch-bus-c...