On March 28, 2020, as COVID-19 cases began to paralyze public life in much of the United States, then-Surgeon General Jerome Adams issued a decree advisory on Twitter: The general public should not wear masks. “There is little or conflicting evidence that they benefit individual carriers in a meaningful way,” he wrote.
Adams’ advice was consistent with messages from other US officials and the US government World Health Organization. Days later, however, top US health leaders changed course. Mask-wearing was soon a strategy to fight pandemics around the world, but whether that strategy has been successful is now the subject of heated debate — particularly after a major new analysis published in January seemed to conclude that masks are becoming more common after remains an unproven strategy to contain the transmission of COVID -19 and other respiratory viruses.
“There is still no evidence that masks are effective during a pandemic,” said the study’s lead author, physician and epidemiologist Tom Jefferson, recently told an interviewer.
Many public health experts vigorously disagree with this claim, but the study has attracted attention in part because of its pedigree: it was published by cochrane, a non-profit organization dedicated to bringing rigorous scientific evidence more directly into medical practice. The group’s highly regarded systematic reviews impact clinical practice worldwide. “This is truly our gold standard for evidence-based medicine,” said Jeanne Noble, MD and associate professor of emergency medicine at the University of California, San Francisco. One epidemiologist described Cochrane as “the Bible.”
The new rating“Physical Interventions to Interrupt or Reduce the Spread of Respiratory Viruses,” is an updated version of a paper published in autumn 2020. It came at a time when debates about COVID-19 were still smoldering among scientists, politicians and the general public.
For some, the Cochrane review provided justification. “Mask mandates were a bust,” said Conservative columnist Bret Stephens wrote last week in the New York Times. “Those skeptics who were angrily ridiculed as cranks and occasionally censored as ‘misinformers’ for conflicting mandates were right.”
Meanwhile, masks continue to be recommended by the US Centers for Disease Control and Prevention, which describes it as “a crucial public health tool”. And some this winter school districts issued short-term mandates to contain not only COVID-19 but other respiratory viruses, including influenza and RSV.
The polarized debate hides a murkier picture. Whether or not masks “work” is a multifaceted question — one that involves a mix of physics, infectious disease biology, and human behavior. Many scientists and doctors say that the Cochrane review’s findings were correct in a strict sense: high-quality studies known as randomized controlled trials, or RCTs, usually don’t show much benefit for mask wearers.
But whether that means masks not Work is a harder question – one that has revealed sharp divisions among public health researchers.
The principle behind masks is simple: when viruses like SAR-CoV-2 or influenza can spread, when droplets or larger particles get from one person’s nose and mouth into another person’s nose and mouth, putting up a barrier can slow the spread. And there’s certainly evidence that surgical masks can block some relatively large respiratory droplets.
However, early in the pandemic, some researchers saw evidence that SARS-CoV-2 was spreading via tinier particles, which is a possibility linger in the air and slip better around or through surgical and fabric masks. “Recommendations for sweeping masks – as many have suggested – will not reduce transmission of SARS-CoV-2,” according to respiratory protection experts Lisa Brosseau and Margaret Sietsema wrote in an April 2020 article for the Center for Infectious Disease Research and Policy at the University of Minnesota.
Her colleague Michael Osterholm, a prominent epidemiologist, was blunt: “Never in my 45-year career have I seen such a sweeping public recommendation from a government agency without a single source of data or information to support it,” he said on a podcast that June. (The Minnesota center is funded by 3M, which makes both surgical masks and ventilators.)
In a recent interview with Undark, Brosseau stressed that she thinks cloth and surgical masks have some protection benefit. But she and others, including Osterholm, have urged policymakers to emphasize tight-fitting respirators like the N95, rather than loose-fitting fabrics and surgical masks. That’s because there’s clear evidence that respirators can effectively capture these tiny particles. “A well-fitting, good-quality respirator captures the virus almost completely, greatly reducing your exposure,” said Linsey Marr, an engineering professor at Virginia Tech who studies airborne transmission of viruses.
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