Nobody said that they don't work. But they are not effective for the average person because a month ago there were so few confirmed cases in the US that it woul

Nobody said that they don't work. But they are not effective for the average person because a month ago there were so few confirmed cases in the US that it would be extremely unlikely that you would ever encounter a COVID positive person. On the other hand, healthcare professionals have to deal with infected patients all day. Suppose a mask is 95% effective on a healthcare professional, and 90% effective on a normal person. But the healthcare professional is in close proximity to a coronavirus patient nearly all the time. Without a mask, there might be 20 chances of infection every day for them. A mask would prevent 19 chances of infection. For a normal person, they might encounter one CoV positive person per day. That means that a mask prevents 0.9 chances of infection. This is much lower than 19. This math is off because I didn't account for mask changings, etc. A healthcare worker should change their mask more frequently than a layperson. After accounting for mask changes, though, I'm sure that the healthcare workers still get more benefit.