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Critics have several issues with the Cochrane Review’s methodology. For example, just six of the 78 trials included were conducted during the COVID-19 pandemic. The others focus on other respiratory illnesses, like the flu. In a February subcommittee hearing, CDC director Rochelle Walensky listed this element as one of the review’s limitations
The authors acknowledge that these studies were “conducted in the context of lower respiratory viral circulation and transmission compared to Covid-19.”
However, beyond other methodology concerns, there are issues with expecting surgical masks to perform in a comparative way to respirators, noted Dr. Chin-Hong. Respirators like N95s and KN95s are designed to prevent airborne infections. Meanwhile, surgical masks are meant to block germ-filled droplets and splatters. Laboratory and observational studies consistently show that respirators outperform surgical masks when it comes to protecting the wearer from COVID-19.8
The Cochrane Review also does not include a random control trial comparing wearing an N95 with no mask.
“That’s a key question,” Dr. Schaffner said. “Maybe that study hasn’t happened, but I’m curious why they didn’t acknowledge in the review that this is a very important question to answer.”