The U.S. Centers for Disease Control and Prevention Wednesday began recommending that Americans wear a cloth mask over a medical mask to slow the spread of Covid-19, along with other options to improve mask fit.
The guidance followed the release of an agency study that found double masking can boost protection from aerosolized particles. Government officials have previously said the CDC was waiting to gather evidence on double masking.
Americans should ensure that masks fit tightly on their face and have layers, both of which improve protection, the agency’s guidance says.
There are several routes to do that, including wearing a disposable mask beneath a cloth mask or choosing a mask with multiple layers of fabric, according to the recommendation. Double-masking with two disposable masks, or with a KN95, isn’t recommended.
“The bottom line is this: Masks work and they work best when they have a good fit and are worn correctly,” CDC Director Rochelle Walensky said at a White House briefing on Wednesday.
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The new study, part of the agency’s Morbidity and Mortality Weekly Report, also examined the efficacy of modifications made to improve the fit of a medical mask.
Either double masking or tightening a mask’s fit reduced exposure to aerosols that could be infectious by about 95%, the research concluded.
“These experiments highlight the importance of good fit to maximize mask performance,” the authors wrote. “There are multiple simple ways to achieve better fit of masks to more effectively slow the spread of Covid-19.”
The findings came from experiments done by the agency last month, which tested how double masking and changes to improve mask fit worked amid coughing, which the researchers simulated.
Knotting the loops of a surgical mask and tucking in extra fabric near the face was found to reduce exposure, as was wearing a cloth mask over a surgical mask.
Surgical masks are designed to ensure a surgical field stays sterile and have became widely worn outside of hospitals during the pandemic. Their protection, however, can be limited by a loose fit like gaps around the sides of the face, the CDC study said.
The authors noted that the findings don’t necessarily translate to a real-world setting. Another key caveat is that the experiments didn’t test other double-masking combinations, such as two cloth masks worn together, they said.