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Federal health officials Wednesday urged Americans to consider wearing two masks as one of several strategies to better protect themselves against the threat of more contagious variants of the coronavirus.

Two methods substantially boost fit and protection, according to a CDC report and updated guidance on its website. One is wearing a cloth mask over a disposable surgical mask. The second is improving the fit of a single surgical mask by knotting the ear loops and tucking in the sides close to the face to prevent air from leaking out around the edges and to form a closer fit.

Both of those methods reduced exposure to potentially infectious aerosols by more than 95 percent in a laboratory experiment using dummies, the report said.

“We know that universal masking works,” said John T. Brooks, medical officer for the Centers for Disease Control and Prevention’s covid-19 response. “And now these variants are circulating … whatever we can do to improve the fit of a mask to make it work better, the faster we can end this pandemic.”

A year after the coronavirus’s arrival in the United States — with the death toll approaching 500,000 — the updated guidance stresses the importance of mask-wearing as one of the best defenses against more transmissible variants, along with social distancing, avoiding crowds and poorly ventilated indoor spaces, and practicing frequent hand-washing.

The guidance comes at a potentially perilous moment, as health officials race to vaccinate tens of millions of people to protect them from more transmissible and possibly more lethal variants but remain hampered by a limited vaccine supply.

It also represents a new administration’s effort to present clear masking guidelines after mixed messaging and the politicization of the issue appear to have bewildered many Americans. Early last year, health officials did not urge their use because of concerns health workers would be unable to get them. Even after health officials reversed course last April after realizing that people without symptoms were driving the virus’s spread, President Donald Trump refused to wear a mask and ridiculed those who did. In part as a result, many Americans still disdain them.

CDC Director Rochelle Walensky acknowledged at a White House briefing Wednesday that some people may be “both tired of hearing about masks as well as tired of wearing them.” She noted that “masks can be cumbersome, they can be inconvenient.”

Conceding the changing guidance since the start of the pandemic, Walensky said that knowledge about the virus has evolved over time.

“The science is clear,” she said. “Everyone needs to be wearing a mask when they’re in public or when they are in their own home but with people who do not live in their household. This is especially true with our ongoing concern about new variants spreading in the United States.”

Walensky said that research shows that coronavirus infections and deaths have decreased when policies mandating masks are implemented. “With cases, hospitalizations and deaths still very high, now is not the time to roll back mask requirements,” she said.

The bottom line, she said, is that wearing any type of mask is better than not wearing one at all.

Until now, the CDC’s recommendation has focused on cloth masks because of worries about a shortage of surgical masks and N95 respirators masks for health-care personnel. But as supply has improved, the agency is providing information about the pros and cons of different masks “so consumers can make an informed choice about what they want to use,” Brooks said. The agency is still not recommending that consumers wear N95 respirators.

President Biden has urged all Americans to wear masks for his first 100 days, and signed executive orders requiring their use on federal property and on planes, trains and buses. Thirty-six state governments currently require people to wear face coverings in public to curb the spread of the coronavirus, according to a tally by AARP. The District of Columbia and Puerto Rico also have mask orders. Three states — Iowa, North Dakota and Mississippi — have lifted such mandates.

Several European nations have also tightened mask regulations: Germany and Austria last month required people riding on public transportation or going to supermarkets to wear more-protective masks, including N95s that filter 95 percent of airborne particles. France has mandated its citizens wear masks that block more than 90 percent of airborne particles in public places. The World Health Organization recommends the public use fabric masks, ideally with three layers.

Brooks and other public health experts say the key takeaway of the new CDC guidelines is mask fit, which improves filtration, or the ability of material to block tiny particles.

“Double masking is one way you can do it,” he said, noting that double masking does not mean double protection. “It may not be the right solution for everybody,” he added. For some people, wearing two masks can impede breathing or obstruct peripheral vision that could lead to a fall and result in injury.

Surgical masks can also be adjusted to make them better fit the contours of the face, Brooks said. The three-ply masks, which may be flat pleated or cone shaped, are not designed to protect against infections from viruses and bacteria but rather to prevent contamination of sterile surgical sites and to prevent blood and other fluids from splashing onto the wearer’s mouth and nose.

Knotting the medical procedure mask where the loops attach to the ear helps the mask fit closer to your face, but it also slightly reduces mask size, he said.

“People with big faces may have difficulty getting the mask to cover their nose and mouth completely when they do the knot, so you really have to look around and find a technique that works well for you,” Brooks said.

The Centers for Disease Control and Prevention on Feb. 10 urged Americans to consider wearing two masks as a protection strategy against the coronavirus. (Reuters)

Studies have shown that fit also can be improved using simple materials, including nylon hosiery around the neck and over either a cloth or surgical mask, and the use of mask fitters — small reusable and adjustable frames or braces worn either as ear loops or behind the head to secure face-coverings tightly on noses.

The CDC conducted experiments last month to test the effectiveness of mask combinations: A three-ply surgical mask blocked 42 percent of particles from a simulated cough, and a three-ply cloth mask blocked 44 percent. But a cloth mask covering a medical mask blocked 92 percent of the particles, the report said.

In a second experiment simulating someone releasing particles during breathing, a dummy wearing double masks and one wearing a knotted/tucked medical mask reduced exposure for an unmasked dummy by 82 percent and 62 percent, respectively. When one dummy was not wearing any masks and the one acting as the bystander wore a double mask or a knotted/tucked medical mask, the bystander’s exposure was reduced by 83 and 64.5 percent, respectively.

But when both dummies wore double masks or knotted/tucked medical masks, the bystander’s exposure was reduced by more than 95 percent in both situations.

Brooks cautioned against generalizing the numeric findings of the studies, however. The experiments used one type of cotton mask and one type of medical mask in a laboratory, “not with human beings,” he said.

Other experts expressed concern that double masking could discourage mask-wearing.

“I would rather people focus on finding one quality mask that meets the mark, versus trying to layer masks and create discomfort, difficulty breathing … or frustration that might lead to no mask at all,” said Saskia Popescu, an infectious-disease epidemiologist and assistant professor at George Mason University.

David Rothamer, an engineering professor at the University of Wisconsin at Madison, has experimented with masks on mannequins in classrooms while studying the best ways to prevent the spread of the virus in college classes. He said he is not a proponent of double masking because it consumes more masks and can also lead to more air leakage.

“The only reason to [wear two masks] is if you can get better fit,” he said.

Linsey Marr, an engineering professor at Virginia Tech who has studied how to maximize mask efficiency, offered these tips for ensuring the best mask fit:

“You should not be able to see or feel any kind of open spots around the edges of your mask, especially around your nose, which is why a metal bridge is so important for fitting tightly around the nose," she said.

“You don’t want gaps around the cheek or chin, really anywhere,” Marr continued. “One way you can check for that is when you are breathing through it, does it feel like air is leaking out of the side? Put your hand on the edge to see if you feel anything. When you breathe in, you should feel suction up against your face.”

Other signs of leakage include eyeglasses fogging up or steamy breath coming from the sides of masks while outside, she said.

Another test involves breathing hard in front of a mirror to see if you blink while wearing a mask, which would indicate leakage from the top of the mask.

If masks fail these tests, Marr said, you should try a different kind of mask. “Peoples’ faces have such different shapes that you can try to find something that can work better for your face,” she advised.