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A Little Evidence that Masks Do Work [1]
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Date: 2023-03-12
My Current Office Mask Stash
I live in South Korea and have not had to put up with much anti-mask sentiment. There have been some people letting their nose poke through when I pass them on the street. I saw a couple of people jogging without a mask when I took research pictures of my entire district in the summer of 2021. I had to remind some of the Uzbeki exchange students to put their masks back on when we went back to in-person classes. The mask mandate just expired at the start of February so I am starting to see a few people here and there in public with a mask on, but I am getting used to it.
One of my current and one of my former colleagues co-authored a piece to explain why, even with initial difficulties and an open travel policy with China, South Korea performed so much better in the pandemic than the US (Dataveillant Collectivism and the Coronavirus in Korea: Values, Biases, and Socio-Cultural Foundations of Containment Efforts). They argued a number of factors explained the general Korean compliance with mask mandates, contact tracing, self-isolation orders to stay at home, and other such measures. As a result, my baseline is that getting vaccinated is a good thing, masks are a good thing, distancing is a good thing. Until the end of 2021, I knew more people who had died from COVID than had even been tested because they had been exposed in Korea. It was some time in 2022 when the number of people I knew who had one or more variants of COVID19 in Korea passed the number of people I knew who had died in the US. Several of the people I know who have had COVID19 contracted it or likely contracted it while travelling abroad.
I spent a lot of time in 2020 and 2021 writing updates in social media urging friends and family to follow precautions, using public data comparing the extent of the pandemic in South Korea and states in the US. It took a long time for my city of about 3 million (Inchon/Incheon) to have deaths out of the single digits, and it still compares very favorably with populations of comparable size in the US.
My home masks ready for when I go to work-I recycle them at the office
The shift from the mask mandate to a limited mandate on public transportation and certain enclosed places feels a little risky, and I am a little nervous about the new semester and large numbers of students crowded on campus again. Into this worry pops reactionary NYT columnist Bret Stephens, who has graced the world with all sorts of misinformation in the past, perhaps most egregiously climate denial, although he referred to himself as agnostic on climate change before admitting a personal experience travelling to Iceland had converted him-like many conservatives, he does not respond the same to things that do not affect him personally.
Now we are treated to his self-justifying anti-mask bias. His piece is titled “The Mask Mandates Did Nothing. Will Any Lessons Be Learned?” The substance of the piece is a trumpeting of the putative findings of the Cochrane meta analysis “Physical interventions to interrupt or reduce the spread of respiratory viruses.” He starts by strengthening his appeal to authority by establishing the bona fides of the study:
The most rigorous and comprehensive analysis of scientific studies conducted on the efficacy of masks for reducing the spread of respiratory illnesses — including Covid-19 — was published late last month. Its conclusions, said Tom Jefferson, the Oxford epidemiologist who is its lead author, were unambiguous.
He also makes sure to drop that the meta-analysis is based on 78 studies, covering some six hundred thousand people. However, he does not go through the findings so much as immediately launch into promoting the sensational unequivocal self promotion of first author Tom Jefferson from his media tour:
“There is just no evidence that they” — masks — “make any difference,” he told the journalist Maryanne Demasi. “Full stop.” But, wait, hold on. What about N-95 masks, as opposed to lower-quality surgical or cloth masks? “Makes no difference — none of it,” said Jefferson.
After the experience of the pandemic, and all of the arguing over masks, that is a bold statement. It is the kind of extraordinary claim that would qualify as requiring extraordinary evidence.
My emergency office mask for when someone drops by unannounced
None of this phases Bret Stephens, though. He accepts it all at face value, assumes everything is proven, “i”s are dotted, “t”s are crossed. Bret Stephens knows in his heart of hearts that he has found the smoking gun that shows
But when it comes to the population-level benefits of masking, the verdict is in: Mask mandates were a bust. Those skeptics who were furiously mocked as cranks and occasionally censored as “misinformers” for opposing mandates were right. The mainstream experts and pundits who supported mandates were wrong. In a better world, it would behoove the latter group to acknowledge their error, along with its considerable physical, psychological, pedagogical and political costs.
His links on the costs, include a medical journal article about “mask mouth,” oral hygiene issues some people develop after prolonged mask use (6-8 hours a day without taking off a mask and not drinking enough water); reference to a study finding that mask use may accentuate social anxiety in some people suffering from the issue; an NPR article reporting on parents wanting their kids not to wear masks; and a social science medical journal article saying that Trump voters were more trait reactive (likely to be triggered by public health mandates and perceive them as taking away their freedom), less conflict averse, and less likely to self-report wearing masks, while Biden voters were the opposite. I can see his argument for the first two as costs, but I do not see how the second two links represent costs, unless some parents not wanting their kids to wear masks and Trump voters being less likely to wear masks is a “cost” of asking people to wear masks.
Stephens does not stop there with his soaring rhetoric, but gets self-righteous, demanding apologies from those who mandated masks, while admitting he will not get them:
And the people who had the courage to say as much deserved to be listened to, not treated with contempt. They may not ever get the apology they deserve, but vindication ought to be enough.
Okay. I guess he is going to apologize to the world for using his perch at the US’ paper of record to be agnostic on climate change in a way the rest of us read as denial? I guess we just we will not get the apology we deserve, but our vindication ought to be enough?
Well, back to the real world, apparently Tom Jefferson has not been entirely straight about his results, either. The article he claims provides no evidence masks “make any difference” is not quite so bold as he has been talking to reporters:
We are uncertain whether wearing masks or N95/P2 respirators helps to slow the spread of respiratory viruses based on the studies we assessed.
From the non-plain language results:
We included 12 trials (10 cluster‐RCTs) comparing medical/surgical masks versus no masks to prevent the spread of viral respiratory illness (two trials with healthcare workers and 10 in the community). Wearing masks in the community probably makes little or no difference to the outcome of influenza‐like illness (ILI)/COVID‐19 like illness compared to not wearing masks (risk ratio (RR) 0.95, 95% confidence interval (CI) 0.84 to 1.09; 9 trials, 276,917 participants; moderate‐certainty evidence. Wearing masks in the community probably makes little or no difference to the outcome of laboratory‐confirmed influenza/SARS‐CoV‐2 compared to not wearing masks (RR 1.01, 95% CI 0.72 to 1.42; 6 trials, 13,919 participants; moderate‐certainty evidence). Harms were rarely measured and poorly reported (very low‐certainty evidence).
Well, the first thing I notice, is that only 12 of 78 studies were about masks versus no masks, so these 15% of the studies analyzed are delivering the major message Stephens is trumpeting. An additional five studies addressed N95 versus surgical masks. To be fair, Stephens does admit, up front, that only six of the 78 studies were conducted under COVID, making this largely a study of other respiratory diseases.
All-in-all, the study’s own abstract is quite a bit more equivocal than Tom Jefferson or Bret Stephens, who told us, “The Cochrane report ought to be the final nail in this particular coffin.” The study’s authors report the need for significant qualifications:
The high risk of bias in the trials, variation in outcome measurement, and relatively low adherence with the interventions during the studies hampers drawing firm conclusions. There were additional RCTs during the pandemic related to physical interventions but a relative paucity given the importance of the question of masking and its relative effectiveness and the concomitant measures of mask adherence which would be highly relevant to the measurement of effectiveness, especially in the elderly and in young children.
Further, they indicate that they really cannot add much clarification to the debate on the basis of their study:
There is uncertainty about the effects of face masks. The low to moderate certainty of evidence means our confidence in the effect estimate is limited, and that the true effect may be different from the observed estimate of the effect. The pooled results of RCTs did not show a clear reduction in respiratory viral infection with the use of medical/surgical masks.
They have limited confidence in their effect estimate, the true result may be different, and their randomized control tests did not resolve uncertainty. It sounds like this handful of studies simply cannot provide the definitive answers Stephens and Jefferson want to project.
On the other hand, the subject of the study is not exactly was is being reported. From their selection criteria:
We included randomised controlled trials (RCTs) and cluster‐RCTs investigating physical interventions (screening at entry ports, isolation, quarantine, physical distancing, personal protection, hand hygiene, face masks, glasses, and gargling) to prevent respiratory virus transmission.
The design of the study was about physical interventions (not masks), so the conclusions drawn would be applicable as well to “screening at entry ports, isolation, quarantine, physical distancing, personal protection, hand hygiene, face masks, glasses, and gargling,” not just face masks. That would mean that the travel bans to and from specific countries and the infamous Title 42 would be included. As a result Stephens could be demanding apologies from all of the people insisting on xenophobic immigration restrictions, although
We found no RCTs on gowns and gloves, face shields, or screening at entry ports.
So, while there is little evidence (and no conclusive evidence) related to masks, there is no evidence related to screening, so I guess Stephens is off the hook there for not demanding any apologies.
I guess I am not alone in my criticisms, though. Before I was able to look up the paper for myself, my biochemist brother forwarded a couple of pieces reviewing this. I mention he is a biochemist not to establish his authority but because he did so in response to me marveling at how the paper passed peer review and was published, using his own personal experience of witnessing how scientific publishers may have other concerns in getting even iffy research out there. He then made the point that the study was not bad per se, but that the first author was seriously misrepresenting it (with the full and willing collusion of media workers like Bret Stephens).
The first piece he shared was “The new scientific review on masks and Covid isn’t what you think” by Kelsey Piper in Vox, subtitled ”A meta-analysis seeks to be the last word on the effectiveness of masks, but finding answers in science isn’t that easy.” She sets out the problem:
Here’s a seemingly simple question with a deeply unsimple answer: Do the masks that so many of us spent more than two years wearing actually prevent the spread of Covid-19? There have been dozens of studies trying to answer that question, and often they point in different directions, or are too small to find the effect they’re looking for.
Her link goes to “Effectiveness of Face Mask or Respirator Use in Indoor Public Settings for Prevention of SARS-CoV-2 Infection — California, February–December 2021,” which studied a smaller population in California across most of a year during the pandemic and found a 56% decrease in likelihood of catching COVID based on self-reported indoor cloth mask use, 66% for surgical masks, and a whopping 83% for those wearing an N95/KN95 mask. That sounds pretty compelling to me as a non-scientist but I am sure Tom Jefferson has better evidence.
Kelsey Piper makes the point that the aggregate result of many studies is needed to draw conclusions, that meta-analysis is a tool for doing that, and that Cochrane is known for doing so reputably for medical questions. Even so, she does temper that by pointing out
But there are a lot of methodological decisions that go into a meta-analysis, and Cochrane brings its own set of assumptions to that table: they tend to exclude many studies as low-quality, and tend to be conservative in declaring that an effect exists.
That sounds reasonable and consistent with the study itself, which narrowed itself to a handful of studies to analyze, and reported that it had little to say about the effect of masks. Kelsey Piper goes on to qualify Tom Jefferson’s credentials and reputation:
I think Jefferson — an Oxford University epidemiologist who has a number of eccentric and flatly nonsensical opinions about Covid-19, including that it didn’t originate in China and may have been circulating in Europe for years before its global emergence — is overstating his case. There is something we can learn from the Cochrane paper, but it’s as much about the process of science as it is about the effectiveness of masks.
She then goes on to make a number of points about limitations of the study in particular that make its findings not terribly compelling. Only 6 of the 78 studies took place during the pandemic-most were about typical flu transmission-and only two specifically related to masks during the pandemic, the rest largely related to hand-washing and other interventions. The weakness is further compounded because the two relevant studies were not related to the effect of wearing masks, but the efficacy of being told to wear masks.
The comparison was a randomized comparison between groups that were told to wear masks and groups that were not. My experience in Korea was that almost everyone ordered to wore masks, but anecdotes from friends and family in the US showed that much smaller populations responded affirmatively to calls to wear masks and it varied widely across different groups. My brother told me about seeing a clear majority of people wearing masks as he went shopping in Chicago, but that number dropping to almost no one wearing masks after he crossed over into Indiana to go shopping. Both populations were subject to federal, state, and local encouragement to wear masks at the time, but some more or less complied and some did not.
Piper goes on to point out that one of the two COVID-related studies, one covering 170,000 people in Bangladesh, had results that suggested a very different conclusion from the meta-analysis. The study examined public announcements and mask distributions and found that the experimental group had about 40% mask use as compared to 10% in the control group. As for the results the meta-analysis cared about:
The result, the study found, was a substantial reduction in the share of people with Covid-19-like symptoms, and in antibodies that would suggest a Covid-19 infection: “In surgical mask villages, we observe a 35.3% reduction in symptomatic seroprevalence among individuals ≥60 years old... We see larger reductions in symptoms and symptomatic seropositivity in villages that experienced larger increases in mask use.”
The other COVID study was in Denmark, comparing a group that did not generally wear masks with one assigned to wear masks, who had a lower but non-significant incidence of COVID infections. That is, the totality of the studies directly related to the effectiveness of COVID mask use covered by the meta-analysis that reported inconclusive results and was promoted as showing the ineffectiveness of masks actually showed the complete opposite: efforts to promote mask use resulted in actual increased mask use and real decreases in the transmission of COVID, whether statistically significant or not. This is not the strongest evidence, but it goes directly against both the meta-analysis findings and how they were reported. Piper reports:
“I was really surprised that the Cochrane group let this go through,” Jake Eaton, a public policy and global health researcher who was the lead researcher on a Cochrane review of childhood nutrition, told me. “The fact it’s looking at masks across different settings and with different diseases makes it really tricky. Cochrane reviews are very good if you really want to assemble the most rigorous evidence and say, ‘Do we have a conclusive signal that this works?’ This is something of a perverse use of a Cochrane review.”
My brother also led me to another piece Yes, masks reduce the risk of spreading COVID, despite a review saying they don’t, authored by C Raina MacIntyre, Abrar Ahmad Chugtai, David Fishman, and Trish Greenburgh. MacIntyre et al point directly to problems with the meta-analysis’s methodology and assumptions about transmission. In addition to the questions raised above, they point to the study assumptions by the meta-analysis that randomized control tests are the best studies and that combining multiple randomized control tests will give an average effect size.
In response to the first issue, they note that randomized control tests are not necessarily the best ways to address every question. Secondly, they note that studies can only be combined in meta-analyses if they are addressing the same question in the same way.
The study assumed all masks provided a respiratory effect, and it combined all sorts of studies with different designs and different purposes, including different types of masks.
This Cochrane Review combined RCTs where face masks or respirators were worn part of the time (for example, when caring for patients with known COVID or influenza: “occasional” or “targeted” use) with RCTs where they were worn at all times (“continuous use”).
Further, they note the meta-analysis only looked at one half of the equation regarding mask usage-the protection for the wearer but not the protection from the wearer of a mask transmitting the virus. They pointed to evidence for the second effect as a meaningful benefit of mask use:
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.
They also point out that different studies in the meta-analysis did not cover the same environments, mixing studies in crowded areas with high transmissibility with others in less dangerous settings. They point back to the rather modest benefits of mask use seen in the Bangladesh study noted above with that had an 11% general reduction in COVID19 transmission and a 35% reduction among those over 60 at greater risk. They then drew a contrast with a hospital study of n95 use that showed a 67% reduction in bacterial infections and a 54% reduction in viral infections. They also point out that seasonal viruses vary from year to year, making the studies combined for the meta-analysis apples and oranges comparisons.
They note that the studies in the meta-analysis are not largely studies of mask efficacy but of the effect of different levels of compliance with calls to wear masks. Any negative conclusions drawn from the meta-analysis amount to the limitations of the advice to wear a mask, not that of mask use itself.
They also point to copious amounts of evidence from other types of studies:
A comprehensive review of the evidence would also include other types of study besides RCTs. For example, a large systematic review of 172 various study designs, which included 25,697 patients with SARS-CoV-2, SARS, or MERS, concluded masks were effective in preventing transmission of respiratory viruses. Well-designed real-world studies during the pandemic showed any mask reduces the risk of COVID transmission by 50–80%, with the highest protection offered by N95 respirators.
Finally, my own comparisons from locations with higher and lower mask usage, show different general levels of effectiveness. This does not hold to the rigor of other types of studies, but is illuminative nonetheless:
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