Here’s an article
Wearing a face mask can reduce coronavirus transmission by up to 75 percent, study says
(as close to a source as I could find)
It is super seeing research like that! The next question to our society is: how do we couple mask usage with another “multiplier” so that people can coexist inside a room and not transmit the virus at all?
The case studies that I have seen demonstrate one person spreading the virus to up to 80% of the other people in a room in 3 hours. Reducing that transmission rate by 75% isn’t actually helpful on its own; in simplest terms, now that same 80% gets infected in 12 hours 🙁.