Face masks are emerging as one of the most powerful weapons to fight the new coronavirus, with growing evidence that facial coverings help prevent transmission—even if an infected wearer is in close contact with others.
Robert Redfield, director of the Centers for Disease Control and Prevention, said he believes the pandemic could be brought under control over the next four to eight weeks if “we could get everybody to wear a mask right now.” His comments, made in mid-July with the Journal of the American Medical Association, followed an editorial he and others wrote there emphasizing “ample evidence” of asymptomatic spread and highlighting new studies showing how masks help reduce transmission.
The research Dr. Redfield cited included a newly published study suggesting that universal use of surgical masks helped reduce rates of confirmed coronavirus infections among health-care workers at the Mass General Brigham health-care system in Massachusetts.
Stemming the Spread
Researchers simulated droplet dispersal from a heavy cough using different types of common masks.
Alberto Cervantes/THE WALL STREET JOURNAL
His comments are the clearest message yet from the CDC, amid fierce debate over facial coverings, fueled initially by shifting messages from federal and global officials about their necessity and then by those espousing individual liberties.
The CDC currently recommends the use of cloth face coverings in public, and several states have made the coverings a requirement for most people in wide-ranging public situations. An analysis published Sunday in the BMJ, a medical journal, found that face coverings are now recommended or mandated in 160 countries to reduce coronavirus transmission.
Researchers from around the world have found wearing even a basic cloth face covering is more effective in reducing the spread of coronavirus than wearing nothing at all. And many are now examining the possibility that masks might offer some personal protection from the virus, despite initial thinking that they mostly protect others.
Experts caution that widespread masking doesn’t eliminate the need to follow other recommendations, like frequent handwashing and social distancing.
In the absence of widespread availability of N95 masks—considered among the most effective but typically reserved for health-care workers—transmission can still be reduced with simple and affordable face coverings, the research shows. A case study by Australian researchers published last week in the journal Thorax found that a three-ply surgical mask made of nonwoven material noticeably reduced droplets dispersed while speaking, coughing and sneezing. The surgical mask proved more effective than two-layer and one-layer cotton facial coverings, the researchers found, noting that efficacy diminished as masks grew thinner.
The study, which analyzed the droplet spread of a healthy volunteer after capturing it on video, hasn’t yet been peer-reviewed. Researchers concluded from their observations that homemade cloth masks likely need several layers—ideally at least three—to prevent the transmission of the virus.
Their findings largely align with a study published last month in the journal Physics of Fluids by researchers at Florida Atlantic University. They found that, of the readily accessible facial coverings they studied, a well-fitted homemade stitched mask comprising two layers of cotton quilting fabric was most effective for reducing the forward spread of droplets. The research was conducted using a mannequin’s head, an air compressor and a smoke generator that mechanically simulated a cough. This study didn’t evaluate leakage from surgical masks.
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The study found that aerosol-size droplets expelled from the mannequin with the double-layered cotton mask traveled forward about 2.5 inches on average, and that most of the leakage escaped from gaps between the nose and face. Loosely fitting facial coverings, including a folded cotton handkerchief with ear loops, as well as a bandanna were less helpful, the study found. With those masks, droplets traveled on average about 1.25 and 3.5 feet, respectively. In contrast, the study found droplets traveled about 8 inches on average with an off-the-shelf cone-shaped mask.
Meanwhile, droplets from an uncovered cough traveled around 8 feet on average, though the study found that they could travel up to 12 feet—double the currently recommended social-distancing guideline of 6 feet.
“It was surprising in a good way to see that a homemade mask could do so well…that we don’t have to get a very fancy mask,” said Siddhartha Verma, one of the study’s co-authors. “A cotton mask can be washed at home and dried. Reusability is becoming important as we go into this for the long haul.”
Dr. Verma and one of his co-authors, Manhar Dhanak, said they are also in the process of putting a laboratory apparatus together to test how much protection various masks might offer to the person wearing them. They plan to study protection against various-sized droplets and particles, as researchers home in on evidence that in addition to large respiratory droplets coronavirus can also be transmitted through aerosol particles that linger in the air.
Exposure is also a focus of researchers now. The amount of virus exposure might influence degree of sickness, according to a review of viral literature and coronavirus epidemiology by Monica Gandhi, a professor of medicine at the University of California, San Francisco. She and her co-authors posit in the research, expected to be published this month in the Journal of General Internal Medicine, that masks provide an important barrier and could lead to a milder infection or even prevent one altogether. While cloth and surgical masks can widely vary, she believes some masks can likely filter out a majority of large viral droplets.