I may not be the head of a globull stink tank but when I see SK, Japan with everyone walking around with a mask and having a fraction of cases compared to other countries, my little simple brain says there might be something there
As a radiation protection technician at commercial nuclear power plants, one of the things I got to do was evaluate how various worker behavior affected the “protection factor” achieved by them wearing a full-face mask respirator. We used an 0.2-micron aerosol and were able to measure the effect on protection factor associated with actions such as talking, grimacing, twisting, etc. None of the plants I worked at would let a worker take credit for respirator use if his or her protection factor fell below 50 at any stage of the evaluation. We only tested full face masks, which provide much better facial seal than any paper mask. Someone who wears a paper mask may occasionally get some tiny protection factor, but I suspect most wearers never receive any sustained protection. So when I see most people wearing paper masks, I attribute any purported benefit to some other factor.