I don't think we can trust people to be sensible, unless they are told in no uncertain terms.
I know somebody who was planning on visiting a new mother whose premature baby is in a neonatal unit.
I had to point out why that was a terrible idea - and not just because her son potentially has it!
Also, looking at the St Patrick's Day revellers and massive concert in cardiff. People won't keep away. My nephews, in their 20s, don't take this seriously because they are "invinsible".