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Aug. 26, 2020 -- In 1910, 10,000 hunters rushed into a region in northeast China that sits on the border with Russia. They were searching for an animal called a tarbagan marmot that made its home in underground burrows there and was valued for its pelts.

Fur was high fashion in Europe. German tradesmen had recently devised a way to dye cheaper marmot pelts to look like more expensive mink and sable.  Prices for marmot quadrupled, sending throngs of foreigners to scour the forests of Manchuria for the shrieking, toaster-sized rodents, which are relatives of squirrels.

These hunters are the reason we are all wearing face masks today.

Instead of following traditional methods used by skilled marmot hunters, the inexperienced newcomers dug the animals out of their underground burrows. This method, historians believe, brought them into contact with sick animals infected with Yersinia pestis, the bacteria that causes the plague -- one of the deadliest human pathogens.

Soon the hunters began dying in droves, vomiting blood and turning purple. The illness was quick and almost universally fatal. Its victims typically died within 2 days. Records show only a single person survived their infection. It was also spreading quickly. No one knew how to stop it.

When bodies began piling up in the streets of town of Harbin, the Chinese emperor sent a 32-year-old doctor named Wu Lien Teh to intervene. Wu had recently graduated from The University of Cambridge England. He was the first Chinese man to attend its prestigious school of medicine. He brought western medicine and its methods to the frontier town, one of the last stops on the newly built trans-Siberian railway, which had greatly expanded trade between Asia and Europe.  The railroad also meant the disease could travel.

Wu arrived on Christmas Eve, 1910. He quickly performed an autopsy on one of the recent victims. The autopsy itself was a radical act because it violated traditional beliefs about how to care for the dead.  To pull it off, he had to convince a local man to let him examine the body of his dead wife, who was Japanese. The autopsy revealed that the disease had eaten holes patient’s lungs. He also found the plague bacteria in the lungs. It was the first time anyone had seen pneumonic plague, or plague of the lungs.

Unlike previous plague epidemics, which had been transmitted to humans by the bites of infected fleas, this disease was spreading from person to person. Wu realized it was being carried through the air, in respiratory droplets from breath. He wrapped the faces of health workers and grave diggers in layers of cotton and gauze to filter out the bacteria, creating the ancestor of the modern n95 respirator mask. He urged people to cover their faces.

Not everyone believed his theories. A well-known French doctor and experienced plague fighter who had arrived in Harbin shortly after Wu ignored his young colleague’s warnings to cover his face when treating patients. His death, a few days later, grabbed international attention.

“That kind of took the world by storm. Everybody sat up and noticed. From then on, for years, masks were globally important in dealing with respiratory pandemics,” says Jeremy Howard, a data scientist and researcher in residence at the University of San Francisco. Howard stumbled across Wu’s story as he led an effort to compile research on face masks earlier this year.

Soon, everyone was wearing Wu’s cloth face coverings. There was even an international design competition for face masks. Wu’s design won.

“It’s interesting how effective his designs were. Stuff we’re now discovering or rediscovering are what he and his team discovered in the decades from 1911 onwards. He basically dedicated his life to fighting respiratory plague,” says Howard.

The outbreak killed more than 60,000 people in 4 months. By March of 1911, it was over, and Wu was widely praised for his efforts that used masks, quarantines, contact tracing, and other actions to control it. In 1935, he became the first Chinese physician to be nominated for a Nobel Prize. Universities around the world -- including Johns Hopkins in Baltimore -- awarded Wu honorary degrees.

Face masks again played a central role in efforts to control the 1918 flu pandemic. But decades later in the West, at least, face masks were forgotten.

History Repeating

Asian countries never forgot the lessons of the Manchurian Plague. In Asia, wearing masks in public is considered a part of good hygiene. Many people keep them at home and wear them in public if they feel ill, especially during cold and flu season. People seen coughing or sneezing uncovered in public are shunned for shirking their civic duty to protect the health of other people.

It’s no surprise, then, that soon after seeing their first cases of COVID-19, in cities like Hong Kong, which was heavily impacted by the first SARS virus in 2003, and in countries like Taiwan, nearly everyone began wearing masks in public.

Those places have logged some of the lowest numbers of COVID-19 cases and deaths in the world. Taiwan, which has a population of nearly 24 million, has officially logged fewer than 500 COVID-19 cases and seven deaths.

To date, Hong Kong, which is densely populated with 7.5 million people, has had 4,700 cases and 78 deaths.

“Hong Kong, you know was a kind of a disaster waiting to happen,” Howard says. The government left the borders open to China, even as infections climbed on the mainland. But people decided to wear their masks. Shops required them for entry. Surveys indicate 98% of people in Hong Kong wore their masks and infections stayed low.

Mongolia, a country of 3 million people bordered by China and Russia, also adopted the widespread use of masks early in the pandemic and has reported just 300 cases and no deaths.

As a data scientist, those numbers impressed Howard. “Statistically, these were very surprising results. Not just anomalous, but requiring deep explanation.” At the time, public health officials here did not encourage mask wearing, fearing that supplies would run out for health workers.

Then Howard found a video on YouTube of a man speaking the words “stay healthy” in a pitch black laser scattering chamber. Without a mask, you see green flecks of light fly toward the camera as the person talks in the dark. With a mask on, there’s nothing to see, giving credence to point: Wearing a mask lowers the risk of spreading the virus.

The creators of the video, which was posted anonymously, turned out to be scientists at the National Institutes of Health and the University of Philadelphia. The New England Journal of Medicine eventually published a letter describing the experiment.

“It became really clear that this is actually a really well-done piece of research,” Howard says, “and it’s very obvious that this piece of fabric is stopping the droplets that transmit disease.”

“It’s all kind of added up to a call to action,” says Howard.

As more research emerged about the effectiveness of masks, Trump announced a change in policy on April 3. He said all Americans should voluntarily wear cloth face coverings, though he muddied the message by saying that he didn’t think he’d be doing it himself.

Though the federal government has declined to issue a mask mandate for the entire country, individual states have taken action. Thirty-four require face coverings in public. Mississippi joined the list on Aug. 4, as cases there have surged.

A July poll by The Associated Press—NORC Center for Public Affairs Research found that 86% of Americans reported wearing face masks when they left the house compared with 73% in May.

The mandates seem to be working. A study in the journal Health Affairs recently concluded that mask mandates in states that have them may have prevented between 230,000 and 450,000 new cases. A recent data analysis by The New York Times found that as COVID-19 cases drop in the U.S., the states that are driving those decreases all have some local mask mandates. Many have also paused or reversed their reopening plans, closing bars, gyms and theaters.

There are however, some people who just won’t be convinced.

Christos Lynteris, PhD, a medical anthropologist at the University of St. Andrews in Scotland, who has studied the social significance of face masks, thinks the reasons for not wearing one are more complicated than party politics.

“It’s a complex phenomenon, with different people approaching it from different perspectives,” he says.

“There are, I think, young people who think that this is not their disease, that it’s a disease for old people, you know, it shouldn’t ruin their lives,” he says.

Lynteris says he recently saw a group of young men trading the same face mask outside an ice cream parlor. The store required a face mask for entry, but the friends only had one mask between them, so as soon as one would come out, he would hand the mask to the next guy who would put it on and go in.

“So they are complying, but you know, they are actually doing something that is extremely dangerous and also a mockery of the effort of an entire society,” he says. “I couldn’t believe my eyes.”

For others, refusing to wear a mask has become a visual symbol of being a free-thinker and nonconformist.

Still others view the face covering as Asian and a tool of communist control, Lynteris says. “You know, Asian masks are for the Chinese, you know, they’re not going to reduce us to mindless masses.”

Howard scratches his head at these attitudes, which he knows exist but can’t fathom.

“It seems about as political to me as putting on a pair of socks. You know, it’s a piece of clothing you wear as a basic hygiene measure,” he says.

Research Is Catching Up

Scientists who study bioaerosols -- the tiniest dried droplets of saliva that can carry viral particles and stay aloft for hours -- have jumped to study the effectiveness of face masks and help answer practical questions, like which fabric is best to use and which design is most effective.

One of them is Linsey Marr, PhD, a professor of civil and environmental engineering at the University of Vermont.

She has been testing different fabrics and fits of face masks and different sizes of droplets -- from the tiny floating aerosols to the fat drops that mimic sputum that fall quickly to the floor after we cough or sneeze.

To do this, she has placed two mannequins about 12 inches apart in a box that looks like a big microwave. The mannequins have been fitted with tubes through their mouths. One mannequin, let’s call it the cougher, is fitted with a nebulizer -- a machine that’s used to turn medicine into a floating mist. Marr uses the same mix of salt water the government requires to test the effectiveness of n95 masks. To generate larger droplets, she uses an airbrush machine and dyes the saline solution red so she can see where it lands. The other mannequin has a tube that gently draws in air, akin to the flow of a breath. She tests them bare faced and then with just one fitted with a mask and then both wearing masks.

The work is still in progress, but she says some things are clear.

First, only n95 masks, the dome-shaped respirators, block the tiniest aerosols, which is why they’re so critical for health care workers who need a high level of protection.

But as the particles get just a little bit larger, around 2 microns in size, “the ones that we think are actually even more important for transmitting disease, almost all of the different fabrics we tested and types of masks block at least half of those,” she says.

And once the particles are up to about 5 microns in size, most fabric masks block about 80% of those, she says.

Marr says if you want a good face mask, the type of fabric doesn’t matter as much as the layers. You need at least two for decent protection. “If you’re doing two layers, the next most important thing is fit,” she says. It’s even more important than the type of fabric you’ve got. Masks should conform closely to your face and completely cover both your nose and mouth.

She said in all her tests, the most effective fabric they found was a microfiber cloth. It blocks something like 80% of even the smallest particles. But the fabric was stiff, and when they put it on the mannequin, there were gaps around the nose and mouth, and in her tests, Marr says it didn’t perform as well as a cotton T-shirt, which they made according to the CDC’s design, and it fit much better.

Marr says the recent controversy over gaiters, stretchy loops of fabric worn around the head, was unfortunate. She’s afraid some people may have given up on them, when it might have been the option they could wear the most consistently. Tests in her lab found they work fine, especially if they’re doubled.

Though Marr’s testing has been comprehensive and well designed, it is somewhat limited because she isn’t working with actual particles of virus. To work with the virus that causes COVID-19, you need a specialized lab called a biosafety level 3 lab. Those labs work under high security to prevent the virus from accidentally infecting the researchers or escaping into the community.

Don Milton, MD, a professor of applied environmental health at the University of Maryland, recently received that high-level clearance for his lab, and he’s just begun to study how the SARS-CoV-2 virus travels in coughs and sneezes. His study is enrolling people who test positive for the COVID-19 infection.

“Our goal is to assess how much virus is being shed into exhaled breath,” says Jacob Bueno de Mesquita, PhD, a post-doctoral fellow who is working on the study in Milton’s lab.

To do that, they will have people cough, sneeze, and speak, with and without masks, into a giant cone Milton designed calls the “Gesundheit machine.”

Results from a different study, which were published in the journal Nature Medicine in May, found surgical masks were effective at blocking viral particles of both seasonal coronaviruses and influenza and concluded that masks could prevent the transmission of those infections.

There have also been case studies that point to the effectiveness of face masks. In one study, two hair stylists infected with COVID-19 in Missouri who both wore masks during their appointments didn’t pass their infections to any of their 139 clients or secondary contacts. Most of their clients were also wearing masks. These are all the same kinds of studies and observations that Wu conducted in China during Manchurian Pandemic of 1911, “of course using the standards of the time,” Lynteris says. Back then, he says, “It’s kind of science fiction stuff.”

Today however, he thinks it should be good common sense.

After masks helped to stop one of the worst outbreaks of infectious disease in history, Lynteris says Wu would be shocked to find that some people still didn’t believe in them.

“As the inventor of this mask, he clearly believed in this very, very firmly,” he says. “He would be appalled.”

Show Sources

Jeremy Howard, researcher in residence, University of San Francisco, California.

Christos Lynteris, PhD, medical anthropologist, senior lecturer, University of St. Andrews, St. Andrews, Scotland.

Linsey Marr, PhD, professor of civil and environmental engineering, the University of Vermont, Burlington.

Don Milton, MD, professor of applied environmental health, University of Maryland.

Jacob Bueno de Mesquita, PhD, post-doctoral associate, Maryland Institute for Applied Environmental Health, University of Maryland School of Public Health, College Park, MD.

“Face Masks Against COVID-19: An Evidence Review,”, April 12, 2020.

New England Journal of Medicine, May 21, 2020.

National Academies of Science, "Rapid Expert Consultation on the Effectiveness of Fabric Masks for the COVID-19 Pandemic,” April 8, 2020.

Associated Press-NORC poll, July 23, 2020.

Health Affairs, August 2020.

MMWR, July 14, 2020.

Nature Medicine, April 3, 2020.

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