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Double masking can block 92% of infectious particles, CDC says

A man wears a double mask as he visits Times Square in New York on December 10, 2020. - US President-elect Joe Biden said he will ask Americans to wear masks for the first 100 days of his administration to curtail the spread of coronavirus. (Photo by Kena Betancur / AFP) (Photo by KENA BETANCUR/AFP via Getty Images via CNN)

(CNN) — Double masking can significantly improve protection, new data from the US Centers for Disease Control and Prevention shows.

Researchers found that layering a cloth mask over a medical procedural mask, such as a disposable blue surgical mask, can block 92.5% of potentially infectious particles from escaping by creating a tighter fit and eliminating leakage.

“These experimental data reinforce CDC’s prior guidance that everyone 2 years of age or older should wear a mask when in public and around others in the home not living with you,” CDC Director Dr. Rochelle Walensky, told a White House briefing.

“We continue to recommend that masks should have two or more layers, completely cover your nose and mouth, and fit snugly against your nose and the sides of your face,” said Walensky

Medical procedure masks like the commonly seen blue surgical masks typically don’t fit securely to faces and create gaps, allowing unfiltered air to escape. A fitted cloth mask can act as a cinch and secures the loose medical mask in place. This improves protection by preventing leakage of unfiltered air and particles, better protecting the wearer and those around them.

Beginning in January 2021, the CDC tested two simple modifications to improve the performance of commonly used masks by using the “double masking” and “knotting” methods.

The study found that ‘knotting’ can improve the overall performance of medical procedure masks. By folding mask edges inward and knotting ear loop strings where they meet mask fabric, the excess fabric is flattened and reduces the gap on either side of the face.

A knotted medical mask can block 63% of particles that could contain coronavirus from escaping, a significant improvement from blocking only 42% of particles when unknotted, according to the CDC’s Morbidity and Mortality Weekly Report published Wednesday.

The study also found that when both an infected and uninfected source were wearing double masks, the cumulative exposure from potentially infectious aerosols of of the uninfected person was reduced by 96.4%. When both people wore knotted and tucked masks alone, the cumulative exposure was reduced by 95.9%.

Both findings highlight the importance of a good fit to maximize mask performance and reduce exposure.

The CDC team used a medical procedure mask, and a three-layered cloth mask for a total of 12 different mask combinations. They performed tests using various combinations of no mask, double masks, and unknotted or knotted and tucked medical procedure masks. They did not test N95 respirators.

When studying ‘double masking’ these experiments used one cloth mask over a medical mask. The researchers did not include any other combinations of masks, such as cloth over cloth, medical procedure mask over medical procedure mask, or medical procedure mask over cloth.

“I want to be clear that these new scientific data released today do not change the specific recommendations about who should wear a mask, or when they should wear one. But they do provide new information on why wearing a well-fitting mask is so important to protect you and others,” said Walensky. “Based on this new information, the CDC is updating the mask information for the public on the CDC website to provide new options on how to improve mask fit.”

Some may see the new CDC research efforts as the first tepid acknowledgement from the federal government that the public needs higher quality masks, that experts and democratic lawmakers have been calling for.

An Axios-Ipsos poll found an all-time high of 72% of Americans say they wear a mask at all times, but some Americans have expressed frustration at the evolving mask guidance responding to the novel coronavirus. Experts point out that ‘novel’ means new, and as scientists and health officials learn more, recommendations may change.

Dr. John Brooks, chief medical officer of the CDC’s Covid-19 response, who worked on the study, described the findings as “new information for consumers to help them really take control of their risk.”

“If you’re going to wear a mask, consider what you can do to make sure that it fits well to improve its performance,” Brooks told CNN.

Masks became an important part of the coronavirus response when it was discovered that the virus could be transmitted by asymptomatic carriers. It was initially a scramble to get people wearing masks last spring, and some experts have spent the last year conducting studies proving masks could prevent the spread of coronavirus. Now that it is known how well masks work, the next step is making them work better, according to Brooks.

“We’ve never had to think about regulating cloth masks,” Brooks told CNN.

There are also efforts in the works to create the first US consumer mask standards.

ASTM International, an international technical standards organization, and the National Personal Protective Technology Laboratory, are working on standards help Americans tell which masks actually work,

The National Personal Protective Technology Laboratory is a part of the CDC’s National Institute of Occupational Safety and Health (NIOSH).

Brooks indicated that the CDC would encourage or recommend the ASTM standards, but didn’t believe the CDC would require them to avoid “creating barriers.”

He does believe having a consumer mask standard in place could move the manufacturing market in the right direction, which is ultimately what is needed to ensure consumer protection.

“An ASTM approval that you’ve met their standard, we hope, will push the industry in the direction of being sure they focus on producing masks that actually do what they’re supposed to.”