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

Double masking can significantly improve protection, new data from the US Centers for Disease Control and Prevention shows.Researchers found that laye...

Posted: Feb 10, 2021 9:32 AM

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.

Double masking and knotting

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.

New data is not changing reccomendations

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.

Consumer mask standards in the works

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."

Oregon Coronavirus Cases

Data is updated nightly.

Cases: 348766

Reported Deaths: 4161
CountyCasesDeaths
Multnomah54797689
Washington37988313
Marion36055444
Clackamas29094304
Lane26966298
Jackson22632300
Deschutes19577123
Umatilla14241144
Linn12380120
Douglas11795240
Josephine9233195
Yamhill8517110
Klamath7709110
Polk715380
Malheur551574
Benton529130
Coos489691
Columbia371343
Jefferson361450
Union313146
Lincoln310638
Wasco281540
Crook274745
Clatsop239529
Baker198028
Tillamook193328
Hood River188337
Morrow181623
Curry178122
Harney108424
Grant97612
Lake89011
Wallowa67012
Gilliam1484
Sherman1463
Wheeler991
Unassigned00

California Coronavirus Cases

Data is updated nightly.

Cases: 4810682

Reported Deaths: 70604
CountyCasesDeaths
Los Angeles147569426398
Riverside3693444990
San Diego3641044163
San Bernardino3563155566
Orange3227415518
Sacramento1576212279
Santa Clara1445181890
Kern1441461605
Fresno1441232051
Alameda1198871374
San Joaquin1018071708
Ventura1005241164
Contra Costa99234982
Stanislaus851571315
Tulare78945951
San Francisco54031645
San Mateo53828622
Monterey50696582
Solano45761334
Santa Barbara44836521
Merced41781577
Sonoma40711402
Placer38902415
Imperial35642764
Kings32369314
San Luis Obispo29653329
Madera23518281
Butte23364260
Shasta23360334
Santa Cruz20861218
Yolo20147247
Marin17581243
El Dorado16960149
Sutter13775169
Napa12808100
Yuba994282
Tehama9298104
Humboldt9102108
Nevada903990
Mendocino752786
Lassen746346
San Benito737372
Tuolumne673993
Lake6506104
Amador537264
Siskiyou442742
Glenn430330
Calaveras381780
Del Norte356141
Colusa301718
Inyo196739
Mono16445
Plumas15756
Mariposa127315
Trinity86011
Modoc6698
Unassigned1860
Sierra1760
Alpine1020
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