A recent analysis of more than 150 studies found that respirator masks, such as N95 masks, are much more effective at protecting users against contracting coronaviruses than surgical or cloth masks.
For the analysis, which was published Monday in The Lancet and funded by the World Health Organization (WHO), researchers reviewed 172 observational studies spanning six continents and 16 countries that were conducted during the new coronavirus pandemic and the SARS and MERS epidemics, as well as 44 comparative studies that were conducted in health care and non-health care settings. SARS and MERS also are caused by coronaviruses, though those viruses are different from the new coronavirus, which causes the disease known as Covid-19.
N95 masks offer wearer more protection
The researchers found that N95 masks on average provided wearers with 96% protection against the coronaviruses that cause MERS, SARS, and Covid-19, compared with an average of 77% protection with surgical masks. According to the researchers, the use of masks reduced the risk of virus transmission by an average of 3% to 17%, with stronger reductions associated with N95 masks than with disposable surgical or similar masks.
The researchers also found that physical distancing of at least three feet reduced transmission risk by an average of 3% to 13%, and greater physical distancing was associated with greater declines in transmission risk. Further, the researchers found that the use of eye protection reduced transmission risk by an average of 6% to 16%.
Experts say the analysis provides evidence that WHO and CDC should recommend health care and other essential workers wear N95 masks rather than surgical masks to protect themselves against the new coronavirus.
Raina MacIntyre, an epidemiologist at the University of New South Wales, said CDC initially had recommended that all health care personnel wear N95 masks to protect themselves against contracting the virus when treating infected patients, but after supplies of those masks ran short in the United States, the agency downgraded its recommendations and said health care workers could wear surgical masks to protect themselves against the virus in most instances.
"It's been disappointing that both the WHO and the CDC have suggested that surgical masks are adequate, and they're clearly not," David Michaels, a professor at George Washington University and former head of the Occupational Safety and Heath Administration, said. "Reliance on surgical masks has no doubt led to many workers being infected."
"Guidelines should be based on evidence, not on supplies," MacIntyre said. "It's like telling an army, 'Oh sorry, we've run out of guns, just take these bows and arrows and face the enemy.'"
A spokesperson for CDC said the agency was unable to address the findings from the new analysis, but added that the agency is always evaluating new research and "adjusts its guidance accordingly" (Mandavilli, New York Times, 6/1; Chu et al., The Lancet, 6/1; Johnson, Associated Press, 6/1; Kelland, Reuters, 6/1).