The general function that masks serve is mitigation rather than absolute protection. The idea that “masks do NOT prevent the transmission of respiratory viruses” based on my understanding evinces the same fundamental misunderstanding of how a virus causes diseases that underlies much of what’s gone wrong in this pandemic.

Becoming “infected” with a respiratory virus is not the same thing as being exposed to it. Nearly everyone’s immune system is capable of fighting off low-level assaults by any kind of pathogenic virus, but by the same token, there is a threshold beyond which nearly everyone’s immune system will succumb to that same virus. So preventing infection is not a binary “1/0” question; it’s more like a sliding scale that goes from 1 to 1M, and at “1”, you don’t even notice that you’ve fought it off and at “1M”, your immune system is overwhelmed and you’re on your way to the ICU and a vent.

The function of the masks is to keep the exposure level closer to “1” than “1M”. Yes, there is presumably quite a bit of leakage through and around the mask, but if you are in an enclosed space for a limited period of time (a grocery store for example) and everyone is in a mask there, the amount of virus in the air will be significantly less than if everyone was unmasked. Much of the time the difference may not be significant enough to matter, but theoretically sometimes it will. Again, this only applies in densely populated enclosed spaces where people are there for limited periods of time. It would be very unlikely to work, for example, to prevent household transmission. And it should be obvious, that it’s not going to make a difference outdoors, except possibly in the most extremely crowded situations imaginable.

It should go without saying that having a gala where the guests are unmasked but the server are masked makes no sense whatsoever from a public health standpoint. As journalist Glenn Greenwald points out, it’s a “grotesque” display of symbolic power and humiliation.

Coronavirus indoor spread is mostly as aerosols against which non-N95 masks are not super-protective, but again, it’s a cumulative set of factors: ventilation, amount of time spent in the space, how many people are in the space, how much virus is being put out by the infected person(s) in question, how robust is the immunity of the people being exposed, mask efficacy, etc. Even a bad mask may reduce by viral exchange by a few percent and that could be enough to be the difference between exposure to an infection-level viral load or escaping infection.

Universal masking is to me just one factor that in some situations probably reduce the total amount of virus in a given airspace, and so could reduce the chances of an exposure becoming an infection. It’s not all or nothing, however. Nothing is all or nothing!

It’s relative, and given that it’s relative, there’s no reason to worry about whether everyone is wearing a mask. If there are 50 people there, and 2 or 3 aren’t wearing a mask, it’s not likely to make an appreciable difference in the overall level of risks, therefore no need to “mandate” masks anywhere, just put out a recommendation and let adults decide for themselves. This applies to almost everything else COVID: nothing should’ve ever been mandated because nothing offered absolute protection, it was always just generally reducing the overall risks within reasonable bounds and that’s best achieved through education, messaging, advisories and leaving people to make their own social cost benefit analyses.