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Wearing a Mask to Prevent Coronavirus: Scientists Know

As the coronavirus passes through much of the United States, scientists are encouraging Americans to adopt some health measures that have been shown to delay the virus: the use of universal masks, society. Target distance, good indoor ventilation, hand hygiene.

Mask wearing has become a particularly divisive and partisan issue in the last few months. Still, in the face of a surge in incidents, 40 states, including recent holdouts like Iowa and North Dakota, are currently setting mask requirements.

There is almost unanimous support among public health professionals for the obligation of universal masks to protect people from viruses and delay pandemics.

“The more people who wear masks, the more protected the community is and the more personally it benefits,” said Dr. John Brooks, Chief Medical Officer of the Centers for Disease Control and Prevention’s Covid-19 Response Program. .. “It’s like a flock effect.”

Dr. Brooks, a recent breaking news architect, states that masks benefit the wearer as well as those around them. According to the CDC, increasing the proportion of people wearing masks by 15% could prevent the need for blockades and reduce the economic loss that could reach $ 1 trillion, or about 5% of GDP. I will.

“If it doesn’t help avoid the shutdown that’s happening, it will certainly help us come down behind this peak and keep things in check,” Dr. Brooks said.

Other experts note that masks do not work on their own. “To control the spread of Covid-19 to the community and protect individuals, we need a multi-layered approach,” said John Volkens, a public health engineer at Colorado State University Fort Collins.

In August, Dr. Volckens held a workshop for the National Academy of Science and Technology Medicine on how to prevent the spread of the virus in the air. “Masks are an important part of that approach,” he said. “It’s definitely a consensus among scientists.”

So what is the evidence to support the use of masks? And what about the Danish study asking whether masks protect the wearer? We asked an expert to review the latest evidence.

The term mask refers to all types of protective facial covers, but their effectiveness varies greatly from type to type. The Gold Standard is the N95 Respirator, which, as the name implies, can block 95% of harmful particles that the wearer can inhale and exhale. Surgical masks are also very effective in filtering these particles.

But experts say that only healthcare professionals need the protection of the gold standard. Doctors and nurses work closely with infected patients for long periods of time, significantly increasing the risk of getting the coronavirus, Dr. Brooks said.

On the other hand, the average person is much less exposed to the virus and can therefore be protected with a well-made cloth, Dr. Brooks said. The best cloth face covers with multiple layers that can trap virus particles (the thickest ones are barely transparent) are as effective as surgical masks in some situations.

The cloth mask is also reusable and durable, and remains effective even after regular washing. The N95 and surgical masks usually “turn into landfills” once worn, Dr. Brooks said.

It is indisputable that N95 respiratory and surgical masks prevent pathogens from infecting others — one of the reasons doctors have traditionally worn surgical masks to protect their patients.

There is increasing evidence that cloth face coverings also block viruses shed by infected individuals during breathing, conversation, singing, and screaming, and control their spread at the source.

This finding became especially important when scientists learned that even asymptomatic people could spread the virus. Over 50% of all infections can be transmitted by asymptomatic people.

Apart from epidemiological studies showing that masks are used more often in countries that have successfully controlled the virus, mask obligations have been shown to significantly delay the virus in US states and healthcare settings, Dr. Volkens said. It was.

All types of masks provide some protection for the wearer, and studies have shown. The exact degree of protection is not yet clear.

“Wearer protection is not 100%,” said Dr. Lina Wen, a former Baltimore health commissioner, about cloth masks. “It’s also why universal masking is important because infected people need to wear it.”

The N95 mask is considered to be the most effective in this regard, followed by the surgical mask. However, there is little evidence of the benefits of cloth masks.

“There was no good research to protect the wearer,” said Lindsaymer, an expert at Virginia Tech on the aerial transmission of the virus. Still, she added, most researchers assume that cloth masks provide at least some protection.

Some studies on wearer protection were conducted in the laboratory under ideal conditions or using mannequins. Mannequins do not capture the more realistic situations in which people wear masks inconsistently or accidentally.

Nevertheless, in one such study, a mask made of four layers of tightly woven surgical gauze was more infected when worn by both parties than when worn by only the infected person. Dr. Brooks said it effectively prevented.

“They worked best together, and the cloth masks worked essentially like surgical masks,” he said. “When I wear a mask, I protect myself as well as others.”

Critics of mask wear measures have long called for randomized clinical trials to establish their effectiveness. However, experts said that while such trials are the standard for drugs and vaccines, they are not ideal for assessing behaviors that people recall.

“Show me a clinical trial that shows the effectiveness of hand washing,” said Dr. Volckens. “And I think we all agree that smoking causes cancer and is bad for you. Is it unbelievable that smoking causes cancer because there are no clinical trials? ? “

Most studies on fabric surface covers have been observational and have investigated whether their use has stopped spreading at the community level. The latest report on CDC masks lists several such studies that confirm the benefits of universal mask obligations.

In one study, two masked hair stylists were symptomatic, but none of the 67 masked clients were infected with the virus. In another example, facial coverings appear to reduce the risk of infection by 70% during outbreaks at the USS Theodore Roosevelt.

It is especially difficult to assess the benefits of a mask to the wearer. “Because we need to be able to measure what’s behind the mask and what goes through the mask and into the mouth,” Dr. Ma said.

A Danish study published Wednesday was a randomized clinical trial assessing whether masks protected the wearer. No statistically significant effect was seen. However, experts said the study had serious limitations. It was carried out when community infections in Denmark were low and masks were far from standard.

“The whole community didn’t work,” said Dr. Volckens.

The number of studies was small, and only half of the subjects wearing masks reported doing so exactly as recommended. Even those who wear it regularly would not have worn it at a restaurant, bar, gym, or at home. Dr. Ma said it is the environment that is responsible for most of the community’s dissemination.

“It’s difficult to actually do these studies,” she said.

In this study, the wearer’s protection was 15%, although it was not statistically significant. But that may be an underestimate, Dr. Ma and other researchers said.

Julian Tang, Professor Emeritus of Respiratory Sciences at the University of Leicester, said: England.

The CDC has been criticized for the face of the mask since the beginning of the pandemic, when it encouraged only those with symptoms to wear the mask. The agency did not recommend the universal use of face coverings until April. (The World Health Organization issued approval in July, even later.)

Dr. Ma said he was initially hesitant to recommend masks because he was concerned about using the high-quality masks needed by healthcare professionals. “I think it took me some time to realize that the healthcare setting and the community have different purposes,” she said.

When dealing with unknown viruses, it’s not surprising that recommendations change significantly over time, Dr. Wen said. “We know more now. I think we should admit that we were wrong,” she said.

Still, she added that changes in guidance should be seen as a sign that the policy follows the latest science.

“For some reason, the change was assembled by some people as public health professionals who don’t know what we’re doing,” Dr. Wen said. “But in practice, as part of the necessary evolution, we need to see this guidance change. This is the basis for a solid public health response.”

For example, it was not initially clear that the virus could be transmitted by the air, especially indoors or by asymptomatic people. As a result, scientists have assumed that the new coronavirus behaves like the coronavirus that causes SARS and MERS.

However, the CDC immediately recommended a mask after it became clear that asymptomatic infection was a major factor. Dr. Brooks said: So are we, and so are our recommendations. “

Similarly, authorities initially recommended masks only to protect people near the infected, as they were “the place where the earliest and clearest data were available.” There is now enough evidence to say that masks also benefit the wearer.

“Our guidance hasn’t changed — we encourage everyone to wear masks,” he said. “What has changed is that we can give you a reason. A personal reason to motivate people.”

All experts have emphasized that the use of masks is the only tool that can delay a pandemic. Social distance, ventilation and hand hygiene are also important.

“None of them are 100% effective on their own,” said Dr. Ma. “But combining them can have a huge impact on the risk of infection.”

Dr. Brooks said masking is also one of the easiest or should be community strategies to adopt, as states across the country are trying to avoid blockades: “Universal masking policies avoid shutdowns. I strongly believe that it will help. “

Wearing a Mask to Prevent Coronavirus: Scientists Know

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