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‘It is very hard to study this topic’: How research sparked questions around masking and COVID — again

A mix of riders, some wearing masks and others not, disembarked from a commuter rail train at South Station on Thursday.Jessica Rinaldi/Globe Staff

You may have thought the question of masking was settled, or at least that we had all agreed to disagree, but no such luck.

The debate over whether masks limit COVID-19 transmission recently reignited after a new review of the research came out, drawing out skeptics and defenders, and — as so often happens — leaving the ordinary citizen befuddled.

Here’s a rundown of the latest debate, and what you can take away from it.

Do masks work?

Yes, they do.

When you tightly cover your nose and mouth with a material that adequately filters the air (such as an N95 or KF94 mask), the likelihood that the coronavirus can go in or out is dramatically reduced. If you’re infected, the virus is unlikely to get out; if you’re near someone who’s infected, it’s unlikely to get into your nose. In that respect, there is little doubt that masks do work.


“We have good evidence from laboratory studies [that] if you’re wearing a mask correctly and you’re in the presence of the virus, the mask will protect you,” said Jennifer Nuzzo, professor of epidemiology and director of the Pandemic Center at Brown University School of Public Health.

But all sorts of questions remain unanswered when you look at populations rather than individuals. What happens when some people wear masks and others don’t, or when people wear masks incorrectly or inconsistently? Does mandating mask-wearing reduce transmission? What is the best way to prevent transmission in the community?

More study is needed to answer those questions.

What prompted the mask issue to arise again?

On Jan. 30, a British outfit known as the Cochrane Library put out a new report on masking. The Cochrane Review, which is highly respected in medical circles, gathers up all the best research on a health care or health policy issue and assesses the knowledge so far, with the goal of providing “more reliable findings to inform decision-making.”


When the Cochrane Review tackled the mask question, it found that “wearing a mask may make little to no difference in how many people caught a flu‐like illness/COVID‐like illness.”

But the review encompassed primarily studies conducted before the pandemic, which examined the spread of influenza. The flu is far less contagious than COVID-19, which could lead to underestimating the effects of masks. The review also mixed studies of health care workers with those involving the general public, and included studies that couldn’t answer the question of whether people actually wore their masks correctly.

“The appropriate conclusion is, we don’t have great evidence showing that masks change infection rates in populations. But we don’t know why that is,” Nuzzo said. “It’s probably not to do with masks themselves, but how they’re worn.”

For example, Nuzzo said, consider the health care workers who wore masks while caring for patients but still got infected. It’s not known where the infection came from. Possibly the worker took off the mask in the break room and was exposed there, or they picked it up from a family member.

“It is very hard to study this topic,” said John Brownstein, professor of biomedical informatics at Harvard Medical School and chief innovation officer at Boston Children’s Hospital. “There’s a lot of variation in the quality of the studies. . . . The Cochrane Review looks at lots of different periods of time and lots of different scenarios. It becomes less clear.”


Dr. Anthony Fauci, former director of the National Institute of Allergy and Infectious Diseases, said many epidemiologists agree that the Cochrane Review “could be a bit misleading.”

“It’s a meta-analysis of a very large number of studies, many of which had nothing to do with COVID, and many of which did studies with masks that were not regularly worn every day and properly,” Fauci said in an interview with the Globe on Monday. “There were only two studies in that entire meta-analysis that were exclusively looking at masks with COVID.”

Even the Cochrane Review authors expressed doubts. “There is uncertainty about the effects of face masks,” they wrote and added that their confidence in their own estimates of mask effectiveness was “limited.”

So why did this create such a stink?

Some of it was social media. Twitter erupted with criticisms. Then one of the Cochrane Review authors was quoted in a Substack article by the Australian journalist Maryanne Demasi, saying of masks, “There is just no evidence that they make any difference. Full stop.”

But as others have pointed out, there’s no evidence that masks don’t make a difference. The big problem is that there isn’t enough evidence, period.

“I don’t think the study is flawed,” Nuzzo said of the Cochrane Review. “You can only review what’s there. The fact that the majority of studies are not even from COVID, not even from the US, is an embarrassment.”

Still, the Substack interview prompted New York Times columnist Bret Stephens last week to scold all those who favored mask mandates, saying they owed the world an apology.


And that unleashed another round of social media outrage and opprobrium.

“It’s become such a polarized topic,” Brownstein said. “I’ve never gotten as much reaction to anything as the mask topic. It’s hard to know why.”

What’s the bottom line? When and where should a person wear a mask?

The basic advice hasn’t changed. Wear a mask in situations where you think you’re at risk of infection, such as a crowded indoor setting, especially during a time when COVID transmission is high.

The results of the Cochrane Review, which looks at populations, shouldn’t affect what individuals decide, Brownstein said.

“Solid evidence supports high quality masks playing a real role in reducing risk,” he said. “Everybody has their own personal risk profile. And that risk profile is also based on the context of where they are.”

The level of that risk is determined by the level of transmission in your community, your own vulnerability to severe illness, the vulnerability of people you expect to come in contact with, and your personal tolerance for risk.

Fauci agreed. “Everyone is different. Everyone’s risk for a complication is different. So there’s no set rule,” he said.

At age 82, Fauci might be considered at high risk for complications from COVID-19 because of his age. But he also has been vaccinated and received two boosters, as well as having been infected once. That puts his immune system in a pretty strong position, he said. So he doesn’t wear a mask in every indoor setting, only if he’s in a crowded place in a region with a high prevalence of COVID-19.


As for Brownstein, because transmission is currently low, he wears a mask only in health care settings. (He walks to work — no need for public transit.)

Nuzzo also doesn’t wear a mask as often as she used to. She doesn’t pull one on just to run into a store, for example. But she does wear it on public transit and in other places where large groups are close together, such as a packed theater.

She seeks to reduce her risk but knows she can’t eliminate it altogether. Vaccinated and boosted, Nuzzo has never had COVID-19 but feels it’s inevitable that she will catch it someday. Still, she wants to postpone that day as long as possible.

Felice J. Freyer can be reached at Follow her @felicejfreyer.