I'm a complete layman here, but I would expect that the "prevent spread" is not binary, it's a spwetrum [0,1]. Thus, even if it does not completely prevent spr

I'm a complete layman here, but I would expect that the "prevent spread" is not binary, it's a spwetrum [0,1]. Thus, even if it does not completely prevent spread, if just a part, or even a smallish part, is prevented, that also helps others. (Same thing in mask discussion. Lots of people dismiss masks because they may not completely prevent an infection; that is stupid, because masks still decrease the probability of infection (and more importantly, spreading to others).