There’s a lot of back and forth going on over a new study that people say suggests masks are useless to stop the spread of an aerosol based virus. The NY Times, which has been a bastion of COVID mitigation skepticism, featured an op-ed by Brett Stephens that’s as misleading as what you can find on Breitbart any given day.
Here’s Dr Tom Friedan:
Masks have been an effective tool throughout the Covid pandemic, despite erroneous claims to the contrary.
The widely cited Cochrane review on masks was poorly done and even more poorly communicated. Regrettably, researchers analyzed the wrong datasets, in the wrong way, and overstated their conclusions—leading to sweeping and inaccurate characterizations.
Many nuances around mask type, setting, behavior, and policy are explained in this helpful piece by @dr_kkjetelina. http://bit.ly/3ErwuNN 3/
The CDC did an excellent review citing extensive evidence that masks are effective, from multiple studies. http://bit.ly/41oDV1W
Vox also provided a good sense of some of the biases and inaccuracies in the Cochrane review and the idiosyncrasies of the lead author: http://bit.ly/3kr4jaX
Although randomized controlled trials (RCTs) are extremely important, especially for many clinical questions, they are not the best method for every scientific question, as I outlined in @NEJM several years ago: https://bit.ly/3m5ZvYM
The question of WHAT masks are being used for needs to be assessed. Where most transmission is in the household and masks aren’t worn in households, then they cannot be expected to prevent that transmission.
What also needs to be assessed isn’t whether a behavior is mandated, but whether it occurs. For example, mandates in an area already using masks at a high level will provide limited incremental benefits, and mandates that are ignored of course don’t reduce spread.
Different masks provide different levels of protection. And “two-way” masking (i.e., both on the person with Covid and the person being exposed) is much more effective than protective masking—it’s a form of source control. Better masks (N95 in particular) control much better.
Given its glaring weaknesses, including limiting to RCTs and inappropriately combining flu and Covid, the only valid conclusion of the Cochrane review is RCTs of masks in Covid found them to be slightly protective, that the absence of evidence is not evidence of absence and that many other studies with excellent methodologies show efficacy of masking is proportional to the quality of masks used, consistency of their use, and risk of Covid in the environments in which they are used.
Community-wide masking is associated with 10-80% reductions in infections and deaths, with higher numbers associated with higher levels of mask wearing in high-risk areas.
Bottom line: Masks work if they are worn in settings where Covid is spreading, and especially if they are higher quality, such as an N95 or KN95.
Of note: Cochrane included only two actual studies of masking during the pandemic. The first, from Bangladesh, showed a marked reduction in infections. The second, from Denmark, suggested a 20% reduction but it had methodological problems and limited power to detect differences.
I wrote about the errors in the flawed Denmark study in November 2020. The shortcomings of the Cochrane review really are shocking.
Originally tweeted by Dr. Tom Frieden (@DrTomFrieden) on February 23, 2023.
I don’t wear one constantly anymore. But I always have an N95 and a KN95 with me and I use it when I’m in an indoor public space with a lot of people when transmission is high. I try to sit outdoors in restaurants and coffee houses whenever I can which is easy since I live in Southern California. I’m sure it ends up being pretty random but I’m not a young person and I am determined to try to live my life while still trying to be conscious of the threats. And I’m not the only one. I’d guess that at least 20% of people in most public places I go on the westside of LA are wearing masks, and many of the workers are too. (I’m happy to try to protect them too. )
Anyway, don’t throw your masks away even if you’re no longer wearing them. And don’t believe this nonsense they are spewing saying they aren’t useful at all. If we get hit with a new airborne virus for which we have no immunity and no vaccines or treatment, which is entirely possible, you’re going to want to have a good mask handy.