Why the scientific consensus on universal mask-wearing to stop the spread of Covid-19 is shifting in the US.
While working in Beijing last year, I regularly bought packs of N95 masks at my local 7-Eleven. Across the city, masks were a common accessory: In packed subway cars and crowded bike lanes, commuters wore them for protection from the smog year-round.
When the coronavirus surfaced in China late in 2019, not only were masks on hand, they were also a familiar tool for fighting a virus: Many people had used them during the SARS outbreak in 2003. Based on this experience as well as government advice, masks quickly became even more widely used, not only in China, but in other East Asian countries.
In contrast, the US, which had little experience with mask-wearing, took a wait-and-see approach. For more than five weeks after community spread was first documented in the US, the Centers for Disease Control and Prevention (CDC) deemed public mask-wearing unnecessary. In early April, it finally reversed its position and advised the public to wear cloth masks in public spaces.
But some experts saw the delay as a mistake even then, arguing that the case for cloth masks — based on evidence from before the pandemic — was strong enough for the CDC to recommend their use earlier.
Now, new research suggests that East Asian countries’ early adoption of masks has played a role in their ability to control the transmission of Covid-19 — and the US government’s hesitation may have cost lives. “If we had masked up sooner, I think we could have prevented a lot of these infections,” says Shan Soe-Lin, a global health specialist at Yale University, who called for universal masking in a March Boston Globe op-ed co-written with Yale epidemiologist Robert Hecht.
The change in CDC guidance led to a jump in mask-wearing in April, and a recent HuffPost/YouGov poll found that two-thirds of American say they always or mostly wear a face mask or other covering when they were near other people in public.
With the nation now reopening, many experts are pointing to a growing body of scientific evidence, including a perspective published Wednesday in the journal Science, supporting universal mask-wearing in health care settings, airplanes, restaurants, and other crowded places with poor ventilation. And based on this evidence, a growing number of experts are arguing that more state and local governments should mandate cloth masks in these places to check the spread of the coronavirus (15 states require them so far).
It’s a remarkable shift for the US to move toward mandatory masks in the span of just a couple months; let’s walk through how we got here.
How the US muddled masks early in the pandemic
When the first case of person-to-person transmission was reported in the US on January 30, the CDC said it didn’t recommend the public use of face masks. US officials were focused on securing masks for health care workers. But in the process, they made contradictory and premature statements that masks were not effective for the public.
On February 27, CDC director Robert Redfield said, “There is no role for these masks in the community,” adding, “These masks need to be prioritized for health care professionals that as part of their job are taking care of individuals.”
In a February 29 tweet, US Surgeon General Jerome Adams further downplayed the utility of masks for the public:
Seriously people- STOP BUYING MASKS!
They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can’t get them to care for sick patients, it puts them and our communities at risk!
— U.S. Surgeon General (@Surgeon_General) February 29, 2020
While officials’ concern that the public would hoard medical masks was warranted given the limited supply, completely dismissing public mask-wearing went against existing pandemic recommendations and scientific studies. In October, the World Health Organization (WHO) published guidelines for a potential influenza pandemic, which would spread through respiratory droplets like the coronavirus.
The WHO guidance reads: “Face masks worn by asymptomatic people are conditionally recommended in severe epidemics or pandemics, to reduce transmission in the community.”
Benjamin Cowling, an epidemiologist at the University of Hong Kong who co-authored the WHO evidence review, says, in a serious pandemic, “countries should definitely throw everything they’ve got, including face masks.” But at the time, the US was too fixated on hoarding to recognize the potential benefits of recommending cloth masks.
Eventually, as cases mounted, the US came to embrace that approach and settled on a solution that wouldn’t threaten the personal protective equipment stockpile. On April 3, the CDC recommended that the general public wear cloth masks, rather than medical-grade masks — N95 respirator masks, which filter a higher percentage or particles, and surgical masks.
Explaining why it shifted the guidance, the CDC cited new research showing asymptomatic people can transmit the virus. However, Soe-Lin of Yale University says the evidence of asymptomatic transmission was already clear enough for the US to recommend mask-wearing much earlier in the pandemic.
In the wake of shifting guidance, at least 15 states now require cloth masks in public places. But the practice is still far from universal, with some businesses now refusing to serve customers who do wear a mask, according to the Washington Post.
Some academics have argued that US culture has continued to be a barrier. Heather Akou, a fashion historian at Indiana University who has researched the politics of face-covering, says, “Unfortunately in the West, we tend to really associate masks with people doing things for nefarious purposes,” rather than as a symbol of health. “I definitely think people see face-covering as something other people do.”
For some Americans who have worn masks, racial profiling has been exacerbated. Asian Americans have reported being harassed for wearing masks and black men have been targeted by the police while wearing them.
The White House has not helped to shift culture. Both President Trump and Vice President Pence have flouted mask recommendations during public appearances over the past few weeks. When the CDC announced the change in guidance, President Trump said, “You can do it. You don’t have to do it. I am choosing not to do it.” He added, “Somehow, I don’t see it for myself.”
The scientific debate over cloth masks
Trump’s resistance to masks may be more about optics than anything else, but the use of cloth masks has stoked debate, not just about their efficacy, but also about how high the bar for scientific evidence should be during a pandemic. Was enough known about the costs and benefits of recommending public cloth mask-wearing for the CDC to do it earlier in the pandemic?
Scientific studies have evaluated surgical and N95 masks, but relatively few have looked at whether cloth masks can stop virus transmission. Ideally, to gauge the efficacy of cloth masks in this pandemic, scientists would use a randomized control trial (RCT) to compare how much Covid-19 patients spread the virus with and without cloth masks. However, such a trial would take precious time and pose ethical problems.
For the WHO influenza pandemic mask recommendation, researchers did not find statistically significant evidence from RCTs for the use of face masks, but from the broader literature, they concluded that masks could slightly reduce transmission, according to Cowling.
The lack of direct RCT evidence for Covid-19 mask-wearing shouldn’t stop countries from deploying them — including cloth masks while medical mask supplies remain constrained, Trish Greenhalgh, a primary health care expert at Oxford University, and her co-authors argue in the British Medical Journal. Indirect evidence suggests that masks have the potential to reduce Covid-19 transmission and — critically — they point out that the benefits probably outweigh the costs: Masks are cheap and the risks of using them are low.
New research looking at surgical masks lends support to their use to prevent virus particles from an infected person from spreading into the air. An April Nature Medicine study of a sample of 10 people infected with a seasonal coronavirus found that people wearing surgical masks did not shed the virus in respiratory droplets or aerosols (smaller droplets), while 30-40 percent of infected people who weren’t wearing masks did shed the virus. The study also found that the surgical masks effectively blocked droplets containing the flu. “There’s no reason to think the masks would work differently for Covid-19,” says University of Hong Kong’s Cowling, who also authored this study.
The effectiveness of cloth masks against this virus depends on how it is spread, which is still under investigation. According to the WHO, Covid-19 spreads primarily through droplets, which are released when someone sneezes, coughs, or talks. However, experts have also argued that Covid-19 is being spread through aerosols.
Cloth masks are most effective at filtering out larger droplets. For instance, a damp cloth almost entirely blocked droplets created by talking in an experiment described in an April New England Journal of Medicine letter to the editor.
Masks can also help filter out smaller aerosols, but to a lesser extent. Household materials, ranging from a scarf to a vacuum cleaner bag, had between a 48 percent and 86 percent filtration efficiency in a study looking at these smaller particles, compared to the 95 percent efficiency rate of N95 masks. A mask’s efficacy will depend, in part, on the material and shape, as well as how snugly it fits on your face and whether it’s covering both the nose and mouth.
“What I worry about is exposure to the smaller particles that are exhaled from talking and breathing and not coughing and sneezing,” says Lisa Brosseau, an environmental health specialist at the University of Illinois at Chicago who co-authored an article in April arguing there was not enough data to recommend that members of the general public without symptoms wear cloth or surgical masks. In an interview, she said she still doesn’t endorse the use of cloth masks because of concerns about how effective they are at blocking those particles. “I don’t have a problem with people wearing masks,” she says, “I tell them to be careful when you wear a mask that you don’t count on them.”
Some experts argue that everyone should have access to high-grade medical masks (N95s) if supplies are secured. But in the interim, many experts are encouraging the public to wear cloth masks as a symbol of collective action against the virus.
“I wear it because it’s effective — it’s not 100 percent effective — but it’s … respect for another person, and have that other person respect you,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN on Wednesday. “You wear a mask, they wear a mask, you protect each other.”
Masks have likely slowed the spread of Covid-19 in East Asia
In addition to scientific experiments in the lab, growing evidence from East Asian countries suggests that masks can reduce the transmission of Covid-19. From Hong Kong to Taiwan, many East Asian governments started promoting mask-wearing soon after the Covid-19 outbreak began.
In contrast to the US, a preexisting culture of wearing masks helped spark rapid mask adoption, in part due to the lasting legacy of SARS. In Hong Kong, for example, “People voluntarily did it rather than people waiting for any government recommendations,” says Chi Chiu Leung, a doctor and former Hong Kong public health official who has advocated for universal mask-wearing during the pandemic.
But the adoption of masks was not entirely straightforward.
The Hong Kong Department of Health recommended the public use surgical masks on January 24 but the government’s ban on face masks, introduced last year during the city’s protests, still held. Hongkongers started wearing surgical and cloth masks despite — or in some cases because of — the ban, according to Cowling. In the city, 97.5 percent of respondents said they were wearing masks when surveyed in mid-February.
Similarly, in Japan, while Prime Minister Shinzo Abe was criticized for a delayed response to the pandemic, some experts credit Japan’s high standards for personal hygiene, including mask-wearing, with helping to bring the virus under control in recent weeks.
Concerns about SARS, the avian flu in 2004, and then the swine flu in 2009 heightened the popularity of masks in Japan, according to a 2012 study published in The Sociology of Health and Illness. Wearing masks became a “risk ritual” in the country, write the study’s authors.
“When we deal with illness or the threat of illness, we use scientific knowledge, but it’s not everything,” says Mitsutoshi Horii, a sociologist at Chaucer College in the UK who co-authored the study. “In Japan, masks actually function in many different ways. Fundamentally, wearing a mask gives people a sense of security — being in control.”
In China, Covid-19 mask-wearing was instinctual to a certain extent as well, but strong government policies also helped to reinforce the public response. Wuhan required the use of masks in public spaces from hotels to parks starting January 22 — a day before the city’s lockdown. One nationwide survey conducted right after the Wuhan lockdown began showed that 98 percent of respondents (half of whom lived in Hubei province, home to Wuhan) were wearing masks when going out.
On January 30, China’s National Health Commission released Covid-19 protection guidelines that called for wearing single-use medical masks in public spaces. The government clearly stated that higher grade medical masks should be left for the use of health care workers.
Even though all of the formerly high-risk areas in China have been downgraded to low-risk, the national government continues to advise people to wear masks when they can’t maintain social distance. Beijing still requires mask-wearing in crowded places like subways and supermarkets.
Some Chinese officials have been vocal in their view that mask-wearing has aided China’s containment of the virus. George Gao, the director-general of the Chinese Center for Disease Control and Prevention, told Science on March 27, “The big mistake in the US and Europe, in my opinion, is that people aren’t wearing masks.”
Other East Asian countries, including South Korea and Taiwan, also very quickly took to masks and have largely contained the coronavirus. A new study, posted on April 10 and still awaiting peer review, suggests this is no coincidence.
The preliminary study, conducted by a team of researchers in Hong Kong and Europe, shows that 12 regions with a preexisting mask culture or Covid-19 mask guidance were all able to limit the spread of the virus and bring cases down more than 60 percent from peak levels. In contrast, regions that didn’t have mask guidance have not been able to achieve those markers of containment. It is too soon to say how significant the role of masks has been, says De Kai, a computer scientist at the Hong Kong University of Science and Technology who co-authored the study, but the correlation is very clear.
Should masks be required in public spaces in the US?
As the US reopens, advocates for masking say everyone should be required to wear them in public spaces to fight the coronavirus. Their reasoning? The virus can be spread asymptomatically, masks decrease transmission, and not enough people are wearing them yet.
Among the advocates is a group of over 100 health experts who signed a May 14 letter and launched the #Masks4All movement calling for governments worldwide to mandate masks for the general public. Several countries and US states are responding; the Czech Republic, Slovakia, and Austria now have masks requirements, and on Friday, Virginia became the latest state to do so.
Two models in the preprint by De Kai and his co-authors show why requiring masks may make a difference. Assuming the use of a non-medical, but high quality mask, they found that if 80 percent of a population wears masks when lockdowns end, along with social distancing, the virus could be eliminated. This scenario would result in 60,000 deaths in a population the size of the UK (66.7 million). If only 50 percent of the population wears masks, cases would be reduced but the virus would continue to spread, leading to 240,000 deaths.
The study also demonstrates that masks are most useful if a country achieves a high level of mask-wearing by day 50 of an outbreak. Some US states have yet to reach that point.
“The expected utility of masks far outweighs the cost,” De Kai says. “Even if the uncertainty was 50-50, which it’s not,” he adds, “when it’s all upside and no downside, you take the bet.”
In order to reach near universal levels of mask-wearing, though, the US may have to require masks rather than just advising their use. “We need 70 or 80 percent compliance to stop the spread especially with the lockdown phasing out,” says Jerome Howard, a data scientist at the University of San Francisco who co-authored an evidence review, “so the current approach [of most states] of just urging people to wear masks is definitely not working.”
On May 27, three University of Pennsylvania professors described in a New York Times op-ed why complementary policies and messaging are also needed to make mask-wearing easy, understood, and normal in the US. “The most obvious path to universal masking is to pass laws and punish infractions,” the Penn researchers write. “But enforcing legal edicts to wear masks in public can be difficult and costly, and amid widespread ambivalence can lead to backlash and even violence. So edicts are not a complete solution.”
As the case for universal masking has strengthened, Cowling emphasizes that masks should be a part of a broader approach to controlling the virus. According to a recent observational study of Hong Kong’s Covid-19 response that he co-authored, near-universal masking is one of several non-pharmaceutical measures — including quarentines, border restrictions, and distancing — that have likely helped reduce transmission. “From our analyses in Hong Kong, it looks like face masks can help but aren’t enough on their own to keep transmission down to a low level,” says Cowling.
“I think it’s important that we don’t give the impression that people can rely on face masks to keep them safe,” he says. “Masks are useful but they are not a magic bullet against coronavirus.”
Lili Pike is a science, health, and environmental reporting (SHERP) master’s student at NYU and a freelance journalist with a focus on China.
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Author: Lili Pike