> but we're missing a crucial number

Exactly. We're lacking a crucial number. So wear a mask.

Or refuse, and enhance the herd immunity, which is the only thing that will ever really slow the virus in the first place. (Like the flu and colds, this virus will be with us forever and cannot be eradicated, because unlike smallpox and the like, this one has both animal and human hosts...)

I rather think "let's go for herd immunity" is something we need to collectively decide. It's a huge decision and impacts everyone. Like many decisions with collective impact, we rightly restrict the rights of individuals to go their own way on it.

Obviously there isn't collective agreement for a mandate. Are you saying the government should impose a mandate without collectively deciding, or even debating?

That points to a tricky, general problem in political theory and one we've struggled with for millenia. I don't have an answer but I do think there's a middle ground between "authoritarian diktat" and "everyone does what the hell they want".