By masks, I presume you mean surgical or cloth masks. FFPs are known highly effective in protecting people both ways against virus this large, more or less ind

By masks, I presume you mean surgical or cloth masks. FFPs are known highly effective in protecting people both ways against virus this large, more or less indefinitely, assuming there's no operational error. Trouble being that apparently USA cannot make enough of them. Mind you, operational error is likely over longer timespans.