A potential COVID vaccine is an example. I doubt you could ethically instruct people to get a shot for such a health experiment. You can require them to get one to use certain services, but bodily autonomy has precedence in my opinion. That is even more relevant for living pathogens.

Being together with other humans is always a health risk if you want to look at it like that. While it might be incredible stupid to not take the lesser risk, you cannot force people to be rational.