We know: a) Masks reduce transmission by physically blocking viruses b) Vaccinated people can contract COVID by breathing in viruses c) Vaccinated people can

We know: a) Masks reduce transmission by physically blocking viruses b) Vaccinated people can contract COVID by breathing in viruses c) Vaccinated people can infect others by breathing out viruses There's no reason to believe that the mechanism in (a) doesn't work for vaccinated people any more than it wouldn't work for people in Vermont or people named Jake, even if there hasn't been a specific study on those subgroups. Yes, vaccinated people are significantly less likely to be infected and to infect others. That doesn't mean it doesn't happen or that a mask wouldn't reduce that risk further. Whether or not it's worth the hassle of wearing a mask is a reasonable question, but that's a risk/reward tradeoff question, not a question of whether or not a mask reduces risk, which is what your claim is.