I don't know - but neither does the Washington Post.  But they pretend like they do.

This is a really great post from the Powerline guys. There's almost no correlation between mask wearing and the RT (i.e. kind of the rate of contagion).  Of course, I have no idea how reliable the data is about the percentage of people wearing masks. But this article is must reading if you want to see how little the media knows about science, or how little they think their readers know about science.

Do Masks Work?