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In today's New York Times

Opinion

Zeynep Tufekci
Here’s Why the Science Is Clear That Masks Work
March 10, 2023


By Zeynep Tufekci
Opinion Columnist

The debate over masks’ effectiveness in fighting the spread of the c****av***s intensified recently when a respected scientific nonprofit said its review of studies assessing measures to impede the spread of v***l illnesses found it was “uncertain whether wearing masks or N95/P2 respirators helps to slow the spread of respiratory v***ses.”
Now the organization, Cochrane, says the way it summarized the review was unclear and imprecise, and that the way some people interpreted it was wrong.

“Many commentators have claimed that a recently updated Cochrane Review shows that ‘masks don’t work’, which is an inaccurate and misleading interpretation,” Karla Soares-Weiser, the editor in chief of The Cochrane Library, said in a statement. “The review examined whether interventions to promote mask wearing help to slow the spread of respiratory v***ses,” Soares-Weiser said, adding, “given the limitations in the primary evidence, the review is not able to address the question of whether mask wearing itself reduces people’s risk of contracting or spreading respiratory v***ses.” She said that “this wording was open to misinterpretation, for which we apologize,” and that Cochrane would revise the summary.

Soares-Weiser also said, though, that one of the lead authors of the review even more seriously misinterpreted its finding on masks by saying in an interview that it proved “there is just no evidence that they make any difference.” In fact, Soares-Weiser said, “that statement is not an accurate representation of what the review found.”

Cochrane reviews are often referred to as gold standard evidence in medicine because they aggregate results from many randomized trials to reach an overall conclusion — a great method for evaluating drugs, for example, which often are subjected to rigorous but small trials. Combining their results can lead to more confident conclusions.
Masks and mask mandates have been a hot controversy during the p******c. The flawed summary — and further misinterpretation of it — set off a debate between those who said the study showed there was no basis for relying on masks or mask mandates and those who said it did nothing to diminish the need for them.

Michael D. Brown, a doctor and academic who serves on the Cochrane editorial board and made the final decision on the review, told me the review couldn’t arrive at a firm conclusion because there weren’t enough high-quality randomized trials with high rates of mask adherence. While the review assessed 78 studies, only 10 of those focused on what happens when people wear masks versus when they don’t, and a further five looked at how effective different types of masks were at blocking t***smission, usually for health care workers. The remainder involved other measures aimed at lowering t***smission, like hand washing or disinfection, while a few studies also considered masks in combination with other measures. Of those 10 studies that looked at masking, the two done since the start of the C***d p******c both found that masks helped. The calculations the review used to reach a conclusion were dominated by prep******c studies that were not very informative about how well masks blocked the t***smission of respiratory v***ses.

For example, in one study of hajj pilgrims in Mecca, only 24.7 percent of those assigned to wear masks reported using one daily, but not all the time (while 14.3 percent in the no-mask group wore one anyway). The pilgrims then slept together, generally in tents with 50 or 100 people. Not surprisingly, given there was little difference between the two groups, researchers found no difference from mask wearing and declared their results “inconclusive.”
In another prep******c study, college students were asked to wear masks for at least six hours a day while in their dormitories, but they were not obligated to wear them elsewhere. Researchers found no difference in infection rates between those who wore masks and those who did not. The authors noted this might be because “the amount of time masks were worn was not sufficient” — obviously, college students also go to classes and socialize where they may not wear masks.

Yet despite their inconclusiveness, the data from just these two studies accounted for roughly half of the calculations for evaluating the impact of mask wearing on t***smission. The other six prep******c studies similarly suffered from low masking adherence, limited time wearing them and, often, small sample sizes.

The only prep******c study reviewed by Cochrane reporting high rates of mask adherence started during the worrying H1N1 season in 2009 in Germany, and found mask wearing reduced spread if started quickly after diagnosis and if a mask was worn consistently (though its sample size, too, was small).

So what we learn from the Cochrane review is that, especially before the p******c, distributing masks didn’t lead people to wear them, which is why their effect on t***smission couldn’t be confidently evaluated.
Soares-Weiser told me the review should be seen as a call for more data, and said she worried that misinterpretations of it could undermine preparedness for future outbreaks.

So let’s look more broadly at what we know about masks.

Crucially, the question of whether a mask reduces a wearer’s risk of infection is not the same as whether wearing masks slows the spread of respiratory v***ses in a community.

To use randomized trials to study whether masks reduce a v***s’s spread by keeping infected people from t***smitting a pathogen, we need randomized comparisons of large groups, like having people in one city assigned to wear masks and not to in another. As ethically and logistically difficult as that might seem, there was one study during the p******c in which masks were distributed, but not mandated, in some Bangladeshi villages and not others before masks were widely used in the country. Mask use increased from 10 percent to 40 percent over a two-month period in the villages where free masks were distributed. Researchers found an 11 percent reduction in C***d cases in the villages given surgical masks, with a 35 percent reduction for people over age 60.

Another p******c study randomly distributed masks to people in Denmark over a month. About half the participants wore the masks as recommended. Of those assigned to wear masks, 1.8 percent became infected, compared to 2.1 percent in the no-mask group — a 14 percent reduction. But researchers could not reach a firm conclusion about whether masks were protective because there were few infections in either group and fewer than half the people assigned masks wore them.

Why aren’t there more randomized studies on masks? We could have started some in early 2020, distributing masks in some towns when they weren’t widely available. It’s a shame we didn’t. But it would have been hard and unethical to deny masks to some people once they were available to all.

Scientists routinely use other kinds of data besides randomized reviews, including lab studies, natural experiments, real-life data and observational studies. All these should be taken into account to evaluate masks.
Lab studies, many of which were done during the p******c, show that masks, particularly N95 respirators, can block v***l particles. Linsey Marr, an aerosol scientist who has long studied airborne v***l t***smission, told me even cloth masks that fit well and use appropriate materials can help.

Real-life data can be complicated by variables that aren’t controlled for, but it’s worth examining even if they aren’t conclusive.

Japan, which emphasized wearing masks and mitigating airborne t***smission, had a remarkably low death rate in 2020 even though it did not have any shutdowns and rarely tested and traced widely outside of clusters.
David Lazer, a political scientist at Northeastern University, calculated that before v*****es were available, U.S. states without mask mandates had 30 percent higher C***d death rates than those with mandates.
Perhaps the best evidence comes from natural experiments, which study how things change after an event or intervention.

Researchers at Mass General Brigham, one of Harvard’s teaching hospital groups, found that in early 2020, before mask mandates were introduced, the infection rate among health care workers doubled every 3.6 days and rose to 21.3 percent. After universal masking was required, the rate stopped increasing, and then quickly declined to 11.4 percent.

In Germany, 401 regions introduced mask mandates at various times over three months in the spring of 2020. By carefully comparing otherwise similar places before and after mask mandates, researchers concluded that “face masks reduce the daily growth rate of reported infections by around 47 percent,” with the effect more pronounced in large cities and among older people.

Brown, who led the review’s approval process, told me that mask mandates may not be tenable now, but he has a starkly different feeling about their effect in the first year of a p******c. “Mask mandates, social distancing, the other shutdowns we had in terms of even restaurants and things like that: if places like New York City didn’t do that, the number of deaths would have been much higher,” he told me. “I’m very confident of that statement.”

So the evidence is relatively straightforward: Consistently wearing a mask, preferably a high-quality, well-fitting one, provides protection against the c****av***s.

It’s also true that the highly contagious Omicron variant is much harder to avoid, especially because even people masking consistently can catch it from others in their social circle. Fortunately, Omicron arrived after v*****es and treatments were available.

Then why all the fuss?

Masks have become a symbol of frustration over shortcomings in the p******c response. Some see a lack of mask mandates or a failure to wear masks as an abandonment of the clinically vulnerable. The p******c’s burden has indeed fallen disproportionately on them.

Others have come to think mandates represent illogical rules. To be sure, we did have many illogical rules: mandating masks outdoors and even at beaches, or wearing them to enter a restaurant but not at the table, or requiring children as young as 2 to mask in day care but not during nap time (presumably, the v***s also took a nap). Some mask proponents and public health authorities have also used weak studies to make overblown or imprecise claims about masks’ effectiveness.

So how should we evaluate an interview in which the lead author of the Cochrane review, Tom Jefferson, said of masks that the review determined “there is just no evidence that they make any difference”? As for whether N95s are better than surgical masks, Jefferson said, “makes no difference — none of it.” It’s no surprise that Jefferson says he has no faith in masks’ ability to stop the spread of C***d. In that interview, he said there is no basis to say the c****av***s is spread by airborne t***smission — despite the fact that major public health agencies have long said otherwise. He has long doubted well-accepted claims about the v***s. In an article he co-wrote in April 2020, Jefferson questioned whether the C***d outbreak was a p******c at all, rather than just a long respiratory illness season. At that point, New York City schools had been closed for a month and C***d had k**led thousands of New Yorkers. When New York was preparing “M*A*S*H”-like mobile hospitals in Central Park, he said there was no point in mitigations to slow the spread.

In an editorial accompanying a 2020 version of the review — the review is in its sixth update since 2006 — Soares-Wiser noted a lack of “robust, high-quality evidence for any behavioral measure or policy” and said that “when protecting the public from harm is the objective, public health officials must act in a precautionary manner to take action even when evidence is uncertain (or not of the highest quality).”

Jefferson, however, said in the interview that “the purpose of the editorial was to undermine our work.” Soares-Wiser strongly denied this, and asserted that her warning in that editorial would apply to this update as well. Jefferson has not responded to emailed requests for comment.

As Marr notes, a respiratory v***s outbreak with even higher death rates would cut these arguments tragically short. We need to be better prepared in many ways for the next p******c, and one way is to continue to collect data on mask wearing, despite the challenges. That, along with an honest assessment of what was done right and what might have been done better, could go a long way in resolving people’s questions and doubts.

Masks are a tool, not a talisman or a magic wand. They have a role to play when used appropriately and consistently at the right times. They should not be dismissed or demonized.

JohnFrim Loc: Somewhere in the Great White North.

EXCELLENT review of the situation. For me it is unfathomable to say that masks don't work. The extent or magnitude of the benefit is highly variable depending on many circumstances, but to say they are completely ineffective is just plain foolishness... or ignorance. Heck, even coughing or sneezing into a folded arm is better than blasting your breath at a person a few feet away from your face.

David Martin Loc: Cary, NC

The Cochrane review (not a study) was not flawed. It was limited by the amount of reliable data available to analyze.

The study concluded:
"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 v***l infection with the use of medical/surgical masks. There were no clear differences between the use of medical/surgical masks compared with N95/P2 respirators in healthcare workers when used in routine care to reduce respiratory v***l infection."
[emphasis added]

In other words, there is no convincing evidence that having the public wear masks reduced the spread of C***d or influenza. Even if studies found that having medical personnel wear masks to be effective, it is not the same as telling the public to wear masks. Medical personnel wear individually-fitted-to-the-face N95 masks and they wear them correctly, which is not the case with the general public.

Perhaps the CDC could have run properly designed randomized controlled studies to find out, but they did not do so, instead issuing broad recommendations based on their own versions of common sense, intuition, best-guess and hoped-for outcomes.

The Cochrane review did not show masks to be worthless, and did not claim this, despite media reports. They simply found a lack of proof that having the public wear masks provided any benefit, while indicating that more high-quality research might reach a different conclusion.