Do masks really protect against COVID-19? Meta-analysis authors want to see more evidence

A new meta-analysis finds that wearing masks during the COVID-19 pandemic—even N95 masks—may not have afforded individuals any more protection against the virus.

Researchers from various prestigious institutions around the world—including the University of Oxford and the University of Calgary—are not saying healthcare workers and the public should give up on masks as protective devices altogether, but rather they call for more study to be done that would definitively answer the question: “Do masks protect people from COVID-19?”

Right now, what scant evidence exists suggests that the answer is unclear, according to the study published by the Cochrane Library, a collection of medical databases.

The study said that “wearing a mask may make little to no difference in how many people caught a flu‐like illness/COVID‐like illness … and probably makes little or no difference in how many people have flu/COVID confirmed by a laboratory test.”

The Cochrane Library study looked at N95s and P2s, which are the European version of N95s.

“Four studies were in healthcare workers, and one small study was in the community,” the meta-analysis said. “Compared with wearing medical or surgical masks, wearing N95/P2 respirators probably makes little to no difference in how many people have confirmed flu (5 studies; 8407 people); and may make little to no difference in how many people catch a flu‐like illness (5 studies; 8407 people), or respiratory illness (3 studies; 7799 people). Unwanted effects were not well‐reported; discomfort was mentioned.”

The meta-analysis elicited immediate blowback in a comprehensive review in The Conversation, a website hosted by media outlets that seek expert commentary and advice about news events. The article’s title: “Yes, Masks Reduce the Risk of Spreading COVID, Despite a Review Saying They Don’t.”

Kevin Kavanagh, M.D., the president and founder of the patient advocacy group Health Watch USA who’s been closely following and analyzing the pandemic from the beginning, cited The Conversation in his rebuttal of the Cochrane Library’s findings.

“Meta-analysis is a less than optimal methodology to apply to the issue of masking,” Kavanagh told Fierce Healthcare. “Almost all included studies varied widely in their methodology, since it is very hard to ethically have a non-masking control group.”

Kavanagh noted that in some of the studies in the meta-analysis, individuals wore masks only part of the time and COVID-19 spread throughout a building.

“Masks worn by an asymptomatic carrier also protect others, but this was not evaluated in most of the studies,” said Kavanagh. “Negative findings are not surprising in a meta-analysis with suboptimal research assumptions and which includes studies with widely varying methodologies.”

Researchers who wrote the meta-analysis in the Cochrane Library looked at 78 randomized control trials having to do with the spread of respiratory viruses, including ones from 2009 about H1N1, and others conducted during epidemic influenza seasons up to 2016. Six were conducted during the COVID-19 pandemic and comprised two from Mexico and one each from Denmark, Bangladesh, England and Norway. They also used data from four ongoing studies that evaluate mask protection against COVID-19.

The studies took place, said the meta-analysis, “in low‐, middle‐, and high‐income countries worldwide: in hospitals, schools, homes, offices, childcare centers, and communities during non‐epidemic influenza periods, the global H1N1 influenza pandemic in 2009, epidemic influenza seasons up to 2016, and during the COVID‐19 pandemic.”

As the study’s title indicates—“Physical Interventions to Interrupt or Reduce the Spread of Respiratory Viruses”—researchers did not limit their investigation to measuring the effectiveness of masks. They also looked at hand hygiene and found that “following a hand hygiene program may reduce the number of people who catch a respiratory or flu‐like illness, or have confirmed flu, compared with people not following such a program (19 studies; 71,210 people), although this effect was not confirmed as statistically significant reduction when ILI [influenza-like illness] and laboratory‐confirmed ILI were analyzed separately. Few studies measured unwanted effects; skin irritation in people using hand sanitizer was mentioned.”

Just how much medical cloth masks protect individuals against COVID-19 fueled debate throughout the pandemic with Leana Wen, M.D., a medical analyst for CNN, famously declaring that they were “little more than facial decorations.” Kavanagh said that “surgical masks will not reliably stop an airborne pathogen.”

The Centers for Disease Control and Prevention (CDC) stated that “loosely woven cloth products provide the least protection, layered finely woven products offer more protection, well-fitting disposable surgical masks and KN95s offer even more protection, and well-fitting NIOSH-approved respirators (including N95s) offer the highest level of protection.”

As the CDC indicates, N95s have been considered the gold standard when it comes to protecting individuals from the aerosolized COVID-19 particles, though there has been some dispute about them as well. Hazmat-type respirators that cover the entire face offer more protection but hinder functionality in a healthcare setting.

They add that “the results might change when further evidence becomes available. Relatively low numbers of people followed the guidance about wearing masks or about hand hygiene, which may have affected the results of the studies.”

Kavanagh said: “After all masking and public health measures stopped SARS-1 in its tracks in Toronto, I would view the Cochrane Library meta-analysis findings with a large degree of skepticism.”