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Wearing a tight-fitting surgical mask, or doubling up on masks, can significantly reduce COVID-19 transmission and slow the spread of new, more contagious strains, according to a CDC report released Wednesday.
Researchers found that if two people are both wearing surgical masks that are knotted and tucked flush to the face — or if both are wearing a cloth mask over a surgical mask — exposure to viral particles is cut by more than 95%.
"The data in this report underscore the finding that good fit can increase overall mask efficiency," the authors wrote. "Multiple simple ways to improve fit have been demonstrated to be effective."
A "simulated breathing experiment" shows surgical masks on their own block 42% of COVID-19 particles for the wearer, and cloth masks block about 44% of particles. Wearing a cloth mask over a surgical mask increased protection for the person wearing the masks, blocking 83% of small particles.
While other recent studies looked at "mask fitters" — a band that goes over a mask to keep it snug to the face — and found they improved performance, the CDC said it believes the best fit comes from wearing a surgical mask covered by a cloth mask.
COVID deaths in the U.S. jumped in November and, though they are declining, are still high. Officials have warned that the U.K.-based variant could ultimately become the dominant strain in the U.S. by March.
These findings emerge among growing concerns about three new, highly contagious COVID-19 variants first identified in the U.K., South Africa, and Brazil. All three have all made their way across U.S. borders.
Regarding the new coronavirus variants, CDC Director Rochelle Walensky, MD, told reporters at a White House briefing Wednesday that the agency currently estimates that 1%-4% of COVID cases in the U.S. were caused by the U.K. variant, also known as B117.
On the mask study, Walensky said the science was already clear that mask requirements can decrease COVID-19 infections and deaths. But, she said, the new CDC research "underscores the importance of wearing a mask correctly and making sure it fits closely and snugly over the nose and mouth."
Walensky said any type of mask offers some protection, "and well-fitting masks provided the greatest performance both in blocking emitted aerosols and exposure of aerosols to the receiver."
Though little was known about mask protection at the start of the pandemic, mounting research provides clear evidence that they work well. A June paper in the journal Physics of Fluids explained that a cough can cause droplets to travel 12 feet within about 50 seconds. With a properly fitting homemade cotton mask made up of multiple layers, those droplets only traveled about 2.5 inches.
An April study in Nature Medicine found surgical masks drastically reduced transmission of both cold and flu droplets. A January paper in The Lancet Digital Health says an increase in mask-wearing in a community would more than triple its likelihood of controlling COVID-19 spread.
Finally, a CDC study released this month found that from March 22 to Oct. 17, 2020, 10 sites in states with mask mandates reported a decline in COVID-19 hospitalization growth rates by up to 5.5 percentage points. Currently, there are more than 40 states and territories with mask mandates.
To ensure proper mask-wearing, the CDC recommendations include:
Choosing a mask that has two or more layers of washable, breathable fabric
Putting the mask over your nose and mouth and securing it under your chin
Knotting the ear loops of a surgical mask, where they attach to the mask, and then tucking in and flattening the extra material close to the face (knotted and tucked masks)
Fitting the mask snugly against the sides of your face, and slipping the loops over your ears or tying the strings behind your head
If you have to continually adjust your mask, it doesn't fit properly, and you might need to find a different mask type or brand.
Wearing your mask under your scarf, ski mask, or balaclava in cold weather
Keeping a spare mask to replace one that becomes wet
Storing wet reusable masks in a plastic bag until they can be washed
CDC.gov: "Maximizing Fit for Cloth and Medical Procedure Masks to Improve Performance and Reduce SARS-CoV-2 Transmission and Exposure, 2021," "New Variants of the Virus that Causes COVID-19," "Decline in COVID-19 Hospitalization Growth Rates Associated with Statewide Mask Mandates -- 10 States, March-October 2020," "How to Wear Masks."
USNews.com: "These States Have COVID-19 Mask Mandates."
Physics of Fluids: "Visualizing the effectiveness of face masks in obstructing respiratory jets featured."
Nature Medicine: "Respiratory virus shedding in exhaled breath and efficacy of face masks."
The Lancet Digital Health: "Mask-wearing and control of SARS-CoV-2 transmission in the USA: a cross-sectional study."
MedRxiv: "Genomic epidemiology identifies emergence and rapid transmission of SARS-CoV-2 B.1.1.7 in the United States."