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Making masks fit better can reduce coronavirus exposure by 96 percent


By now, most people have received the message that wearing a face mask is one way to help stop the spread of COVID-19. But now health officials are taking the masking message a step further: don’t just wear a mask, wear it well.

A study by the U.S. Centers for Disease Control and Prevention found that taking steps to improve the way medical masks fit can protect users from about 96 percent of the spray particles that the coronavirus spreads. This as long as both people wear masks. But even if only one person wears a tight-fitting mask to fit perfectly, the user is protected from 64.5 percent to 83 percent of potentially virus-carrying particles, researchers report Feb. 10 in the Weekly Morbidity Report and mortality.

“I know some of you are tired of hearing about masks, and also of getting tired of wearing them,” CDC director Rochelle Walensky said Feb. 10 during a White House meeting. But scientists learned last year how masks can be effective in protecting people from catching COVID-19, he said. "The bottom line is this: masks work and work best when they fit well and are used correctly."

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That message is increasingly crucial as the most transmissible coronavirus variants, including those first detected in South Africa and the United Kingdom, begin to spread more widely in the United States (SN: 2/5/21).

Many studies have already shown that masks reduce the amount of spit particles that can spray other people when a person breathes, speaks, coughs or sneezes (SN: 26/06/20). Still, photos and videos show that air and drops often escape from the tops, sides, and bottoms of inappropriate masks. “Even a small gap can degrade the performance of your mask by 50 percent,” says Linsey Marr, an environmental engineer at Virginia Tech in Blacksburg.

Good masks have good filtration and a good fit, she says. "Good filtration removes as many particles as possible and a good fit means there are no leaks on the sides of the mask, where air and viruses can seep through."

Several recent studies have shown that some fairly simple measures to improve fit also reduce aerosol emissions. These measures include the use of ear protectors, pantyhose, or mask accessories or putting a fabric mask over a medical mask.

These studies have shown that wearing a mask protects other people from what the user throws away. But John Brooks, an infectious disease physician and the CDC’s chief medical officer of the COVID-19 emergency response, and his colleagues wanted to know if those tricks to improve mask fit had any effect on carrier protection.

Thus, investigators set up two mannequins facing each other six meters away. A mannequin served as a source, “exhaling” through a tube of saltwater aerosol particles of a size that could carry the coronavirus. (No viruses were used in the experiment.) The other mannequin was the receiver.

The researchers measured how many drops of saline reached a nozzle of the receiving manikin representing the nose and throat. In some experiments, the team put medical masks on only one of the mannequins. In others, both wore masks. The team tested two scenarios to make the mask fit better: tie the ear ties close to the mask and tuck the ends in to eliminate the side openings; and wear a cloth mask over the medical mask.

Researchers at the U.S. Centers for Disease Control and Prevention have tried two tricks to improve the fit of medical procedure masks: put a cloth mask over the medical mask (left) or tie the ear ties and tuck the ends of the mask (right). Both reduced the amount of particles reaching the artificial throat of a mannequin compared to an inappropriate mask or no mask.CDC

CDC mannequin wearing two masks and masks to tie and put on tipsResearchers at the U.S. Centers for Disease Control and Prevention have tried two tricks to improve the fit of medical procedure masks: put a cloth mask over the medical mask (left) or tie the ear ties and tuck the ends of the mask (right). Both reduced the amount of particles reaching the artificial throat of a mannequin compared to an inappropriate mask or no mask.CDC

In each setting, the result was compared to not wearing any masks.

When the receiver wore an inappropriate mask, the amount of droplets reaching his throat was reduced by 7.5 percent. When the source wore the mask, the receiver’s exposure was reduced by 41.3 percent. And when both mannequins wore masks, the exposure to particles was 84.3 percent lower than without a mask.

That’s pretty good. But not as good as it could be. When the receiver wore a knotted, tucked-in mask, his exposure was reduced by 64.5 percent. And when both mannequins wore the masks tied and knotted, the protection was even stronger: the exposure fell a whopping 95.9 percent.

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Wearing a fabric mask over the medical mask further improved the fit. When only the receiving mannequin wore the double mask, it was protected from 83 percent of the particles. And when both mannequins were folded into masks, 96.4 percent of the particles were blocked so they wouldn’t reach the receiver’s nozzle.

Those data show that “mask fit is what really matters and there are many different ways to improve mask fit,” says David Rothamer, a mechanical engineer at the University of Wisconsin-Madison College of Engineering.

Rothamer and colleagues tested devices called mask mounts or mask straps: rubber or plastic frames that fit over the mask by molding closer to the face. Only one medical mask filters about 20 percent of the aerosol drops that come out of the mouth, slightly protecting the others. With a mask assembler in place, 90 to 95 percent of the drops were leaked, Rothamer and colleagues reported on Jan. 4 on medRxiv.org. That report has not yet been reviewed by other scientists. The CDC team has not tested the mask mounts, but that level of leakage should also help protect the user.

Stacking masks beyond two masks probably won’t improve filtration and can stifle voices and make breathing difficult, says Monica Gandhi, a doctor in infectious diseases at the University of California, San Francisco. “No more than two. Leave yourself here, please. "

Mannequin with loose mask and tighter maskAerosol particles can drip from openings where medical masks do not fit the face (left as shown on a mannequin). But a mask assembler used on the medical mask, like the one developed by researchers at the University of Wisconsin – Madison, can prevent that leak (right).Scott Sanders

She and Marr proposed the double-masking strategy to improve the fit of the medical mask on January 15th. The medical mask material is electrostatically charged, which can repel microbes in addition to filtering out particles. The fabric mask helps reduce gaps in the sides and top of the medical mask. Although the CDC study tested the fabric mask over the medical mask, Gandhi says the order may not matter.

It hasn’t been tried to fold into fabric masks, but Gandhi says it’s probably not useful. "I do not see any point. It can improve the fit, but it doesn't improve the filtering ".

There are many simple ways to improve the fit of masks, says Emily Sickbert-Bennett, an epidemiologist and head of infection prevention at the University of North Carolina Medical Center in Chapel Hill. A sleeve of pantyhose on a medical mask improved filtration by up to 80 percent, she and her colleagues reported Dec. 10 at JAMA Internal Medicine. A mask assembler made with elastics, as well as devices known as ear protectors or ear protectors, also worked well. In unpublished work, researchers have also confirmed that putting a fabric mask over the medical mask works well.

Beyond the issue of adjustment, the CDC report also illustrates how important it is for everyone to wear masks, says Sickbert-Bennett. "The best way to double-mask is when you and the person you're interacting with wear a mask."

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