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CDC study finds 2 masks increase protection against COVID-19

The CDC released new guidance Wednesday stating that wearing a cloth mask over a surgical mask is one way to achieve a higher degree of protection

cdc how to layer masks february 2021 guidance covid-19 ppe

The CDC included this graphic in new guidance for increasing the effectiveness of mask use in protecting against COVID-19 exposure.


Peter Krouse

CLEVELAND, Ohio — The Centers for Disease Control and Prevention released new guidance on Wednesday that states wearing two masks can be one way to achieve a high degree of protection from the coronavirus.

The CDC reported that it performed “experimental simulations” in January that assessed the effectiveness of two masking scenarios. One looked at “wearing a cloth mask over a medical procedure mask.” A second involved knotting the ear loops of the medical procedure mask at the edges of the mask and then “tucking in and flattening the extra material close to the face.”

The modifications resulted in a reduction in exposure to simulated aerosol droplets of 95% or greater when both the receiver and the source of the droplets used the masking options, according to the report, which was released Wednesday morning.

“These laboratory-based experiments highlight the importance of good fit to optimize mask performance,” the report states.

One important reason for wearing a well-fitted mask is that air can escape around the edges while breathing in and out, thus reducing the effectiveness of the mask fabric.

The report also discussed studies that looked at “mask fitters,” which can be solid or elastic and are designed to be worn over a mask and secured with head ties or ear loops.

“The results indicated that when fitters are secured over a medical procedure mask, they can potentially increase the wearer’s protection by (90 percent or greater) for aerosols in the size range considered to be the most important for transmitting SARS-CoV-2.”

Another study indicated that placing “sheer nylon hosiery material” around your neck and pulling it up over a cloth or medical procedure mask “significantly improved the wearer’s protection by fitting the mask more tightly to the wearer’s face and reducing edge gaps,” according to the report.

Last month, Dr. Monica Gandhi, professor of medicine at the University of California at San Francisco, and Linsey Marr, a professor of civil and environmental engineering at Virginia Tech University, released a report recommending two options to improve mask efficiency.

One was to wear a tightly fitting cloth mask over a surgical mask, stating that the surgical mask “acts as a filter and the cloth mask provides an additional layer of filtration while improving the fit.”

A second option was to wear a “three-layer mask with outer layers consisting of a flexible, tightly woven fabric that can conform well to the face and a middle layer consisting of a nonwoven high-efficiency filter material (e.g., vacuum bag material).”

The CDC report offers several caveats to its findings, including that they should not be “generalized to the effectiveness of all medical procedure masks or cloths masks nor interpreted as being representative of the effectiveness of these masks when worn in real-world settings.”

Face masks have become an important tool for controlling the spread of the coronavirus although early on in the pandemic they were not viewed by many medical experts as a necessary.

The view began to change as it became apparent that the virus was not only spread by large droplets but also by tiny aerosols that could linger in the air, said Chris Beyrer, professor of epidemiology at the Johns Hopkins School of Public Health.


(c)2021 The Plain Dealer, Cleveland

Read more: EMS1 Associate Editor Rachel Engel looks at expert advice and answers frequently asked questions about double mask-wearing in the article “Doubling up: Are 2 masks better than 1?

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