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February 16, 2021

CDC Studies Underscore Continued Importance of Masks to Prevent Coronavirus Spread

Author Affiliations
  • 1Consulting Editor, JAMA Health Forum and JAMA
JAMA Health Forum. 2021;2(2):e210207. doi:10.1001/jamahealthforum.2021.0207

As new, more contagious strains of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are spreading in the United States, the Centers for Disease Control and Prevention (CDC) has issued new information and guidance on mask wearing, as well as data about the effects of mask mandates and assessing compliance with mask mandates at universities.

Wearing a face mask, along with other mitigation measures such as social distancing and hand-washing, is expected to remain a cornerstone of defense against the virus in the months ahead, even as a growing number of US residents become vaccinated.

“The science is clear: Everyone needs to be wearing a mask when they are in public or when they’re in their own home but with people who do not live in their household,” CDC Director Rochelle Walensky, MD, MPH, said at a February 10 White House briefing that highlighted a new report with evidence about the importance of a snug fit and proper positioning of masks on the face. “This is especially true with our ongoing concern about new variants spreading in the United States.”

The report presents new data from experiments by CDC researchers that assessed how different strategies to improve fit affect masks’ ability to block aerosolized particles released during a simulated cough from a pliable elastomeric “source headform” and to reduce exposure to particles emitted during simulated breathing by a “receiver headform.” The size of the experimental particles was designed to mimic the conditions under which SARS-CoV-2 is spread from person to person.

The studies compared the effect on particle transmission of wearing no mask, a single cloth face mask, and a single medical procedure mask. They also measured the effect of 2 strategies to promote a snug fit: wearing a cloth mask over a medical procedure mask; or knotting the ear loops of the medical procedure mask together where they attach to the mask, then tucking in and flattening the extra mask material close to the face. Either approach substantially reduced particles emitted through the mask and reduced exposure of the mask wearer.

The researchers reported that wearing any type of mask works significantly better than going maskless, and well-fitting masks provided the best performance in both blocking aerosol emissions and aerosol exposure to the receiver. Compared with wearing no mask at all, an unknotted medical procedure mask alone or a cloth mask alone blocks approximately half of the particles from a simulated cough, a knotted and tucked medical procedure mask blocks 77.0% of the cough particles, and a double mask with a cloth mask covering a medical procedure mask blocks 85.4% of the cough particles.

Furthermore, when both the source and the receiver wear masks modified to improve fit, the receiver’s exposure is reduced by more than 95% compared with no mask at all.

“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.

The new data reinforce the CDC’s guidance that everyone 2 years or older should wear a mask—one with 2 or more layers that completely cover the nose and mouth and fits snugly against the nose and the sides of the face—when in public and at home around nonresidents of the household or when someone in the home is sick.

Most US states, US territories, and the District of Columbia have some type of mask mandate in place, but more than a dozen states do not. On January 31, the CDC announced an order requiring that (with certain exceptions) masks be worn while using any form of public transportation or while inside any transportation hub, such as airports; seaports; and train, bus, and subway stations. The order, which went into effect on February 2, makes refusal to wear a mask a violation of federal law, enforced by the Transportation Security Administration and other authorities.

The report on the importance of face mask fit was followed by 2 new CDC studies also released last week, on the effectiveness of mask mandates to curb hospitalization for coronavirus disease 2019 (COVID-19) and compliance with mask mandates at universities.

In 1 study, the researchers measured weekly hospitalization rates at 10 sites in states that had implemented statewide mandates requiring mask-wearing anywhere outside the home or in all stores and food establishments between March 1 and October 17, 2020. At those 10 hospitals, the growth in the rate of hospitalization for COVID-19 among adults aged 18 to 64 years decreased by up to 5.5 percentage points 3 or more weeks after the mandates took effect, compared with the 4 weeks before mask requirements were implemented.

The declines in hospitalization growth rates less than 3 weeks after the mask mandate took effect “are consistent with the incubation period of SARS-CoV-2,” the researchers noted, “long enough to identify an association between mask mandates and COVID-19–associated hospitalization growth rates.”

The second, separate study estimated the proportion of persons wearing masks and wearing them correctly at 6 university campuses with mask mandates. Based on information on mask use recorded by trained student observers, the researchers found high levels of compliance: 85.5% of 17 000 observed persons wore masks, and 89.7% of these mask-wearers did so correctly, translating to an overall rate of correct mask use of 76.7%.

The data also revealed potential areas for improvement. Correct mask-wearing varied by mask type, from 96.8% for N95-type masks and 92.2% for cloth masks to 78.9% for bandanas, scarves, and similar face coverings.

“Colleges and universities can use direct observation findings to tailor training and messaging toward increasing correct mask use,” the researchers said.

The researchers noted that universities can use trained student volunteers to collect substantial amounts of data about mask use on a weekly basis and then use the information “to tailor and evaluate the effectiveness of messages and education to reinforce and increase mask use and to identify locations with lower adherence for policy enforcement.”

As the post-holiday surge of COVID-19 cases has eased and the number of vaccinations is increasing, some states have started to roll back mask mandates, but it is “absolutely” too early to do so, said Walensky, when asked about the issue on NBC’s “Meet the Press” on Sunday.

“We can’t let our guard down,” she said.

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Article Information

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Stephenson J. JAMA Health Forum.

Corresponding Author: Joan Stephenson, PhD, Consulting Editor, JAMA Health Forum (Joan.Stephenson@jamanetwork.org).

Conflict of Interest Disclosures: None reported.

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