The Cochrane Database of Systematic Reviews, a respected biomedical journal, surprised the public recently with a peer-reviewed article raising doubts about the effectiveness of wearing face masks and respirators during the pandemic. An author of the study, Tom Jefferson of the University of Oxford, declared of face masks in an interview, “There is just no evidence that they make any difference. Full stop.”
Not so fast.
First, definitions. A face mask or surgical face mask has gaps at the sides, and the filter materials vary widely, so they do not provide full protection. A surgical mask might prevent droplets from reaching the nose or mouth, but it cannot protect well against smaller airborne particles. Respirators, such as the N95, have a tight fit against the face and far more efficient filtration that can stop smaller particles, so they are far more protective.
When the covid-19 pandemic began, it was feared the virus spread in larger droplets when people coughed, sneezed or sang in a choir. This was the reasoning behind social distancing — the droplets should fall to the ground within six feet. But we now know that covid particles can be much smaller and hover in the air for an hour or more. Through gaps in a surgical mask, they can reach the nose or mouth. But a respirator is more likely to stop them from being breathed in or out.
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Dr. Jefferson and his colleagues set out to measure, using a mountain of data, whether physical methods such as masks and handwashing can interrupt or reduce the spread of respiratory viruses. The new report is an update to an earlier review of scientific research, drawing data from 78 different studies, including 11 new randomized controlled trials involving 610,872 participants. Six of the new trials were conducted during the covid-19 pandemic, but the overall data spans earlier periods with high levels of virus, such as the influenza epidemic of 2009, as well as periods when viral levels were relatively low. The authors acknowledged that drawing conclusions was hampered by “high risk of bias” in the trials, and “relatively low adherence” with the interventions being scrutinized.
Looking at all the data, the researchers expressed doubt about the effectiveness of face masks and respirators. Compared with no mask, “wearing a mask may make little to no difference in how many people caught a flu-like illness” or “COVID-like illness,” and “probably makes little or no difference in how many people have flu/covid confirmed by a laboratory test.” Moreover, they said, compared with wearing face masks, wearing respirators “probably makes little to no difference” in how many people get the flu or a respiratory illness.
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Dr. Jefferson did not answer our request for comment. He told health-care commentator Maryanne Demasi, “There’s still no evidence that masks are effective during a pandemic.” His remarks have been amplified in major news sources.
But the Cochrane study has been criticized for several big flaws. A commentary published by the Center for Infectious Disease Research and Policy at the University of Minnesota noted that it used the traditional definition of virus transmission through symptomatic coughing or sneezing that spreads larger droplets, and suggests it did not focus sufficiently on the key risks of small-particle, airborne transmission. The Cochrane authors also “incorrectly combined studies where people wore masks or respirators infrequently with those where they were worn all the time,” the commentary points out. There has also been separate criticism of a Bangladesh study on masks that comprises more than half the population data in the new trials examined by the Cochrane review.
Here is the bottom line: Loose-fitting face masks and surgical masks have a purpose, but when it comes to covid transmission, they are like wearing goggles with holes. Respirators are far superior in a viral pandemic, given what is now clear about airborne particles and the role that asymptomatic infection has played in transmission. Wearing face masks — but especially respirators — in crowded public enclosed spaces with poor ventilation is undoubtedly better than nothing. A study by the Centers for Disease Control and Prevention concluded that “consistently wearing a face mask or respirator in indoor public settings reduces the risk of acquiring SARS-CoV-2 infection.”
The pandemic has shown that the transmission route from one person to another is the air we breathe. Effective methods to block the virus, particularly respirators, are widely available. It is just a matter of using them.
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