As we discussed yesterday, the issue of mask wearing has become both politically charged in the US partisan political climate and a matter or real controversy among public health experts. There have also been hints, inferences from different countries’ mitigation strategies and some initial studies suggesting that mask wearing is not only effective but possibly more effective than even some advocates of their use anticipated.
Let me try to walk through some of the ins and outs of this debate.
First, here’s an article that is very current among mask skeptics. It’s a review by two bona-fide experts, Dr. Lisa M. Brosseau and Dr Margaret Sietsema, writing back on April 1st, a veritable lifetime ago in COVID19 terms. It was published by the Center for Infectious Disease Research and Policy at The University of Minnesota.
The gist is that there’s little to no scientific evidence that masks are effective for the population at large and that what protection there might be is minimal at best. Additionally, they argue that mask-wearing may create a false sense of security that leads people to relax more effect mitigation strategies like distancing and hand washing. So the net effect of mask-wearing may actually be more infections rather than fewer.
If you read the report closely however a few points emerge.
First, it’s not evidence that masks are not effective – few studies really show this or demonstrate it in any clear way – but a lack of evidence for their efficacy. Second, they focus heavily on health care workers, both for available studies about what works and doesn’t and for the standards we should apply for efficacy. Finally, they take a very binary approach to efficacy. They work or they don’t.
These are all important points. But it is important to understand what they mean in context. One of the reasons there is no evidence that public masking works is that it’s really hard to test. Without a full-blown epidemic it is hard to test the proposition in a robust and meaningful way. So the lack of evidence in this sense isn’t the end of the story.
There’s also threat and context.
We don’t have people take medicines that have no demonstrated efficacy. That’s because you shouldn’t take medicines (often they have real side-effects or risks) that don’t work and in general we have ways to test them to see if they do work. Mask skeptics argue that masks are similarly not indicated. That’s good advice. But at the moment we have a deadly epidemic disease and no medicines or vaccines. So there’s a different risk benefit analysis. The downside of shutting down the national economy is vast in almost every dimension. The risks of mask-wearing at scale – libertarian preening notwithstanding – are minimal. So the lack of hard scientific evidence that they reduce transmission is less dispositive than it might be in other contexts, especially since the lack of evidence is significantly tied to the fact that we haven’t had either the opportunity or much incentive to test it.
The calculus for health care workers isn’t the same as for the population at large. Health care workers have sustained and intense exposure. To make that viable they need protection that radically reduces if not altogether eliminates the risk of transmission. So masks that still get you infected 30% of the time don’t come remotely close to cutting it. That’s not the calculus for society at large. Most people aren’t in constant close contact with infectious patients. Equally important, for society at large the impact of reducing everyone’s risk by 30% has big consequences as these mitigations magnify out across society. It’s simply a different standard.
Let’s take an example. There’s a coffee shop and if I go in there every day for a week there’s an 80% chance I’ll get COVID. If I wear my mask, let’s say that percentage drops to 40%. With those numbers I’m definitely not going into the coffee shop ever. You probably feel the same way. But across society that reductions of transmission is a game changer. The standards for individual risk and societal risk are different.
These are all good arguments. But as I’ve noted above there is important context arguing for different standards of evidence and contrary arguments. There are some cases though where the mask skeptic argument just breaks down, in my untrained opinion, into throwaway lines and non-probative anecdotes. In early March, at one of New York City’s COVID press conferences, Public Health Commissioner Oxiris Barbot was asked why New Yorkers shouldn’t wear masks when clinicians did. Barbot noted rightly that there weren’t enough to go around and that health care workers came first. But then she argued that they would give people a false sense of security. She described seeing a masked New Yorker with his mask pulled down so he could smoke a cigarette. That’s dumb certainly. But it doesn’t really address the question.
In the CIDRAP article noted above the authors noted Wuhan as evidence that widespread masking doesn’t work. “Sweeping mask recommendations—as many have proposed—will not reduce SARS-CoV-2 transmission, as evidenced by the widespread practice of wearing such masks in Hubei province, China, before and during its mass COVID-19 transmission experience earlier this year.”
This simply doesn’t follow. Mask wearing may be more commonplace in China than it is in the US. By few people who weren’t actively sick were wearing masks before the outbreaks began. Mask wearing accelerated massive in mid-January and was mandated in the second half of January. By late February the outbreak had slowed dramatically. This certainly doesn’t prove the efficacy of masking. There were other critical and probably more important mitigations, like radical reductions in mobility, forcing people to stay almost entirely in their home, disinfections, etc. But it certainly doesn’t disprove the efficacy masking. It’s just a non-sequitur, and enough of one that it seems like conclusion driven reasoning.
Here are a few studies in preprint (prior to being peer-reviewed) which take up the masking issue. We don’t have much in the way of studies at the moment. So as you’ll see they tend toward mathematical modeling and reviews of existing evidence.
Face Masks Against COVID-19: An Evidence Review
“COVID-19 transmission risk factors”
The strongest argument for mask usage is that there is a good commonsense argument that widespread mask usage at least limits transmission. That’s why health care workers wear the much more robust n95 masks in clinical settings. So even if people wear lower quality masks and don’t use them as reliably there’s still possibly some benefit. Critically, there’s little downside. It’s not wrecking the economy. It’s not a useless drug that could that could trigger a cardiac event.
More information to come.
