I guess it depends on the person. They may have an underlying health condition that could easily put them at high risk for developing severe complications like pneumonia or bronchitis. (And they may have kept it a secret from you.) Or, they may regularly come into contact with someone who has preexisting health conditions and/or is older than 60.

I think the best thing to do is apologize and explain why you snapped (if you haven't done so already).

Some people are needlessly worrying, while others have valid concerns. However, in general, I think it's okay to say you do not want to talk about coronavirus. You do not have to give a reason if you don't want to. You can just politely say, "I'd rather talk about other things."

Sorry this happened, though. I know that sometimes certain things can get irritating for us and the last thing we want to do is talk about them. But if someone is seriously worrying or angry about it, you can still offer help. Just say something like, "how about we forget about the virus for now and go do [something] or [something else]."