I’ve been avoiding the subject of Covid masking during the resurgence of debate after that recent meta-analysis, because there’s just so much selfish bunk infusing that debate, so really I just want to point out one thing.
In a thorough critique of the analysis by C Raina MacIntyre, Abrar Ahmad Chughtai, David Fisman, and Trish Greenhalgh for The Conversation, the authors make a particular point along the way.
Face masks and respirators work in two ways: they protect the wearer from becoming infected and they prevent an infected wearer from spreading their germs to other people.
Most RCTs in this Cochrane Review looked only at the former scenario, not the latter. In other words, the researchers had asked people to wear masks and then tested to see if those people became infected.
A previous systematic review found face masks worn by sick people during an influenza epidemic reduced the risk of them transmitting the infection to family members or other carers. Preventing an infection in one person also prevents onward transmission to others within a closed setting, which means such RCTs should use a special method called “cluster randomisation” to account for this.
Data from a RCT of N95 respirator use by health workers showed even their unmasked colleagues were protected. Yet some of the trials included in the review did not use cluster randomisation.
Michael Schulson for Undark , although giving the analysis more credit, makes much the same point if only briefly.
Few of the studies took place during the Covid-19 pandemic, instead looking at infections during cold and flu seasons. And the majority of the studies only looked at whether masks and respirators protect the wearer from getting sick — not whether they reduce the odds that a sick mask-wearer will infect other people.
The thing is, the single most consistent piece of advice and explanation throughout the pandemic has been, “My mask protects you, and your mask protects me.” Whatever else was being said about masks, whatever else was being argued over, I heard this again and again and again.
For the much-ballyhooed meta-analysis not to even take this aspect into consideration (it should be noted, as Schulson does, that the lead author of the meta-analysis also has written for a libertarian group “broadly opposed to public health restrictions during the Covid-19 pandemic”) makes it all the more ridiculous that people are waving it around as if it tells us much of anything at all.
(It doesn’t help, according to MacIntyre, et al., that the meta-analysis didn’t fully take into consideration whether or not people were actually wearing their masks—in fact its authors “acknowledged compliance with masking advice was poor in most studies”—which means that at most for such studies “you can only conclude that the mask advice didn’t work”, not masks themselves.)
Whatever the degree of protection afforded me by my own mask, mine is for you and yours is for me. Masking is a form of mutual aid, where we do for each other regardless of what it does for ourselves. This is why it was a public health measure, not a piece of personal advice.