Donald Trump told Fox News on Wednesday that he, the president, looked pretty good in a mask. Trump, it turns out, was never necessarily against wearing masks to slow the spread of the pandemic disease Covid-19, despite multiple statements to that effect. No, no. “People have seen me wear one,” Trump said. “It was a dark black mask, and I thought it looked OK. Looked like the Lone Ranger.” (The Lone Ranger’s mask covered his eyes; masks to prevent the spread of a virus should cover the nose and mouth.)
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This statement was the culmination of a massive shift in messaging—and in science. In the early days of the pandemic, the World Health Organization, the Centers for Disease Control and Prevention, and even WIRED warned people against using masks. They wouldn’t protect people against getting the disease, all those organizations said, and supplies looked short for the personal protective equipment that health care workers were going to need when the pandemic got bad.
What a short, strange trip it’s been. The disease has been in the United States for half a year, and in that time face coverings went from being discouraged by the world’s top public health officials to being encouraged by them—and from being opposed by US political leaders affiliated with the president to being accepted, if not demanded. Even the staunchest conservative political leaders now recommend that people wear masks in most public places and wherever maintaining a discrete 6 feet of social distance isn’t possible. Senate majority leader Mitch McConnell and former vice president Dick Cheney—not exactly avatars of the progressive left—have both made pro-mask statements. After months of opposition, even conservative opinion-haver Sean Hannity has joined the mask-wearing cause.
That change comes on the cusp of being too late. The SARS-CoV-2 coronavirus has roared back to life across the country. Only three states neither require nor recommend masks. Public health experts now agree (the CDC came around in April, the WHO much later) that even though scientific uncertainties remain, masks are a key ingredient in the mix of practices and policies necessary to slow the spread of the disease. They’re the only way to keep the embers of the economy warm as shutdowns and shelter-in-place orders return, and as more people get sick and die from a disease with few treatments, no vaccine, and no cure.
The story of how and why the pendulum swung is an object lesson in the ways public health sometimes diverges from medicine, and how both fields learned to listen to practitioners of a third—the once-obscure science of aerosols, of teeny-tiny particles flitting through the air.
For all the mysteries that remain about Covid-19, the disease was even more opaque in the early months of 2020. Public health officials around the world responded to it as the descendant of two earlier pandemics also caused by coronaviruses—Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS). SARS hit Asian countries particularly hard, and several of them developed playbooks ready to deploy for the next time. These included mask wearing. (In Japan, for example, a culture of wearing surgical masks both to protect wearers against diseases and to prevent spreading them has existed since at least the 1918 flu pandemic.) When early signs of a new respiratory disease started appearing in China in late 2019, Taiwan deployed its equivalent of the US Defense Production Act to produce more masks; army personnel actually went to work in mask-making factories there to crank out supplies.
But that didn’t happen in Europe or the United States. The US federal government had well-documented difficulties building its supply of PPE, forcing health care workers to go begging as makers desperately tried to fill orders, vamping until the White House invoked the Defense Production Act to accelerate mask production in April. “The word that we got was that we were struggling to make sure we get personal protective equipment, including masks, for the health care workers, so the initial recommendation was: Don’t put masks on, because we’re going to be taking them away from health care workers,” says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. “That understandably got interpreted as, we didn’t think masks were of any benefit.”
Some of the messaging from public health officials was even more explicitly opposed, though. In late February, CDC director Robert Redfield testified before the House Foreign Affairs subcommittee and was asked if healthy people should wear masks. “No,” Redfield responded. The day after that, US surgeon general Jerome Adams tweeted “Seriously people—STOP BUYING MASKS.” Fauci himself, in early March, told a Senate committee that the general public didn’t need to wear them because Covid-19 wasn’t widespread enough.
The WHO was even more explicit in its advice: Tightly-fitted N95 masks, which filter out particles as small as 0.3 microns, are for health care workers dealing with sick patients, and they’re in critically short supply. Masks made of other materials—surgical masks made of a synthetic nonwoven, meltblown textile, layers of different kinds of cloth, and so on—can gap at the sides and don’t, on their own, fully protect people from getting infected. More quietly, public health experts worried that if people started wearing masks, they’d overestimate their level of protection and get careless. The science was blurry, but the message had to be clear: No masks for civilians.
“There was the concern that when people wore masks, were people going to continue to wash their hands and follow all the recommendations? Most of my earlier recommendations were focused on people who were sick, because [we thought] if you wear the mask, the greatest benefit is for someone who’s sick,” says Nahid Bhadelia, head of the special pathogens unit of the National Emerging Infectious Disease Laboratories at Boston University. “Very truly, I think that a big reason why public health folks did not recommend widespread use of masks in the public was we were running out of masks in the health care setting.”
But even before Redfield’s testimony in late February, there were hints in the science that this strategy was simply wrong. A few researchers were saying that people who didn’t seem sick—who sometimes might never get sick—were spreading the virus. One report out of Anyang, China, described a family of five who appeared to have been infected by a relative with no symptoms who had recently traveled to the center of the epidemic in Wuhan, 400 miles away. Another study, later published in Science, suggested that before Wuhan officials imposed a strict lockdown, the virus had been spreading in stealth among people with mild or no symptoms. The researchers estimated that more than 80 percent of infections were therefore going undocumented. “These findings help to explain the lightning-fast spread of this virus around the world,” they would later write.
That’s a problem for a lot of reasons. Infectious people could be anywhere, spreading the disease without any indications. Telling people to stay home if they feel sick, or checking them for fever before entering an office or school, would be of little help in stanching the spread of the disease.
It also meant that everyone would have to rethink the mechanism for how the germ spreads. People sometimes pick up respiratory viruses from surfaces like door handles or cutlery—so-called fomites. Another main route is usually droplets people cough or sneeze into the air. But no symptoms means no coughing, which means no droplets.
As the weeks went by, evidence began to accumulate that the virus also spreads through exhalations from infectious people—whether or not they feel or know they are sick. On March 4, a study published in the Journal of the American Medical Association found the virus stuck to the air vent blades in a Covid-19 patient’s room in Singapore. The next day The New England Journal of Medicine published a report of Germany’s first Covid-19 cluster: four people who got sick after being exposed to business associates with no noticeable fever or cough—including one who had recently arrived from China—and later tested positive.
The inferential logic, then, was this: Anyone could be a source of transmission. And the best way to cut that down was masks that minimize not so much the inhalation of those aerosol particles but their exhalation.
If it were true, it would flip the standard advice. A mask might not protect the wearer against getting sick from inhaling aerosolized virus (though it might cut down the overall viral dose, potentially lessening their chances of getting infected or the severity of the illness). But a mask—any mask, didn’t have to be an N95—could reduce the amount of virus a wearer, who is infectious but does not know they are ill, gives off just from speaking, not coughing or sneezing. That opened a path for civilians to mask up without parasitizing the supply of N95s. They could get surgical masks, or even homemade cloth ones. The idea wasn’t to stop the virus from getting in but from getting out.
“That’s when I started thinking that we really need masks on everyone,” says Linsey Marr, a Virginia Tech researcher who studies the dynamics of viruses in the air. “My view on this changed as soon as I started to hear about asymptomatic or presymptomatic shedding of the virus.”
She wasn’t alone. Dozens of other aerosol scientists around the world also began to sound the alarm. They’d been saying since the mid-2000s that respiratory viruses like influenza could be transmitted in the infinitesimal particles people give off from talking or even breathing. In February 2019, a team of engineers at UC Davis had even shown that talking louder and singing made a person emit more of these “expiratory particles” than speaking in a more subdued tone. Aerosol studies had also shown that the closely related coronavirus that caused the SARS outbreak in 2003 could be carried on rising plumes of warm contaminated air—sickening more than 300 residents of a housing complex in Hong Kong. To many in the aerosol field, it was a reasonable assumption that this new coronavirus, which invades human cells via the same receptor, might behave the same way outside the body, too. You just had to look for it.
But there was a problem. People emit streams of saliva and lung gunk in a vast continuum of sizes, and measuring microscopic ones that float in the air is trickier than measuring larger, visible droplets that quickly fall to the ground. Instruments that can detect airborne particles have only been around for a few decades, and they’re not common in laboratories. Aerosol experiments often have to be done in a clean room, to reduce any background interference from the atmosphere. They require a certain kind of expertise in engineering, chemistry, and physics, and tend to draw researchers from those fields.
Droplets and aerosols lie on either side of a mostly arbitrary and almost infinitesimally fine divide. But in terms of the people who study them, the divide goes well beyond mere social distance; they don’t even use the same language. To aerosol scientists, any particle—liquid or solid, nanometers to micrometers wide—is an aerosol if it’s suspended in the air. To other scientists, size matters; aerosols are small, under 5 microns, and bigger particles are “droplets.” That single fact has been the source of so much confusion these past few months. (But for the purposes of clarity, at WIRED we are using the more generally understood dichotomy: aerosol, small; droplet, big.) “People are very resistant to the idea of aerosol particles carrying the disease,” says William Ristenpart, a researcher at UC Davis whose lab did the volume-of-talking research. “There’s definitely siloization. They certainly didn’t teach me anything about virology in engineering graduate school, and my medical colleagues are not taught anything about aerosolization.”
Medical researchers are more accustomed to looking for droplets, both because they’re literally visible and because studies from the 1930s describing them form the basis of respiratory disease transmission chapters in most medical textbooks. So when a new pathogen emerges, public health officials, who almost unanimously come from medical or medical-adjacent backgrounds, tend to reach first for a droplet-driven explanation. “It’s been that way forever because droplets are what you can see,” says Kimberley Prather, an atmospheric chemist at UC San Diego who studies how viruses can become airborne out of ocean surf. “The aerosols are there—for every drop you visibly see when someone coughs, there’s 100 to 1,000 times more aerosols produced. And now we can measure them. But that work has been slow to be accepted by the medical community.”
Covid-19 heated up that conflict. In early March, officials from groups within the White House and the Department of Health and Human Services wanted to put together a team of experts to consult on the pandemic. They asked the heads of the National Academies of Sciences, Engineering, and Medicine to put together a committee; members included physicians, zoologists, immunologists, virologists, genetic epidemiologists, bioethicists, former FDA officials, and statisticians—but no aerosol scientists.
The committee’s chair, a physician and health policy researcher named Harvey Fineberg, told WIRED that when his committee was asked to summarize the evidence on aerosol transmission and the effectiveness of cloth face masks, they consulted with many aerosol experts. But he agrees that the field has long been ignored by most medical professionals. “That’s not unique to these disciplines—in any field new knowledge doesn’t instantly and uniformly permeate. Rather, it gets taken up very gradually” Fineberg says. “What’s distinct here is that the whole process has been vividly exposed because of the press of this epidemic. It’s really showing the urgency and disability of the problem.”
Even as new reports in March showed that infectious particles of the new coronavirus could float in lab-generated aerosols for up to three hours, and that a single sneeze could propel them up to 25 feet, WHO officials in daily press briefings and in tweets held the droplet doctrine line. During an April 3 teleconference, 36 aerosol researchers and infectious disease control experts tried to convince WHO officials that airborne transmission was playing a much larger role in spreading the coronavirus. The WHO didn’t budge.
“There was very strong pushback that the evidence was too weak,” says Lidia Morawska, a leading aerosol researcher at the Queensland University of Technology, who organized the meeting with WHO officials after seeing large numbers of Italian health care workers dying despite adhering to all the available recommendations regarding hand-washing and protective gear. She found the WHO’s response exasperating because she knew there was no way to humanely conduct the kind of experiment that would prove unequivocally that SARS-CoV-2 could infect people through respiratory aerosols. It would involve putting healthy people in one room and Covid-19 patients in another, with only an air vent between them. And you’d have to do it in large enough numbers to reach statistical conclusions. No ethical body would sign off on such a study.
“It is an impossible situation,” Morawska says. “Even if there’s no perfect proof, the WHO has a responsibility for the life and health of people. And the precautionary principle should always be in place if there’s a potential risk. And there’s definitely a potential risk here.”
Marr, who also attended the meeting, put it more bluntly: “The WHO is driven not just by science but also by political considerations. There are some strong personalities there who are just anti-airborne transmission. They just accept that large-droplet transmission is happening and somehow there’s a higher burden of proof for airborne transmission.”
(As of publication, a representative from the WHO had not responded to requests for comment.)
People like Fineberg think the WHO fell victim to a classic scientific fallacy—that the absence of evidence is evidence of absence. “When the WHO said there’s no aerosol spread, that was an utterly misleading statement,” says Fineberg. Granted, he says, public health officials are often called upon to do the difficult work of making black and white declarations and recommendations based on information that’s as gray as it can be. In this case, though, he says, “They were definitive in the wrong direction.”
Despite the WHO’s reluctance to urge masking and accept the aerosol idea, other countries got the message. Including the US. Sort of.
On April 3, the same day Morawska and Marr were making their case to the WHO, the CDC put out new guidelines, recommending that people wear cloth or fabric face coverings (not “masks”!) when entering public spaces. The guidelines were pretty sparse—no information on how much transmission such coverings could block or what the most effective kinds of materials might be, though they did post a video with instructions for how to make a face covering out of a T-shirt, starring the surgeon general. CDC officials called them “an additional, voluntary public health measure.” Trump emphasized this last point in a press briefing that day. “It’s voluntary; you don’t have to do it,” he said. “I don’t think I’m going to be doing it.”
It was the opposite of good public health practice. Calls for 100 percent adherence rarely work, but unclear calls to a mixture of muddled behaviors never work. Now, to be fair, none of the science was 100 percent, either. Cultural uptake of mask wearing in the US was outpacing both the science and the expert statements, even if it felt a little like just a way to perform how much we care for each other. Nobody had good data on the effectiveness of homemade masks when used against any respiratory virus, much less how they’d perform against Covid-19.
This is tough to study. Part of the problem is that how well a mask works depends on three things: its filtering capacity, how well the wearer keeps it in place, and the role that particle size plays in transmission. “Multiple routes of transmission can happen simultaneously, and it’s very hard to separate those,” Marr says. Of course, scientists have tried—taping over subjects’ nostrils and mouths, outfitting them in N95 masks or face shields. “We’ve been trying to figure this out for decades for influenza, with millions of dollars and specialized studies,” Marr says. “I doubt we’ll know it for SARS-CoV-2 for many years, if ever.”
But even if scientists can’t yet put an exact figure on what sizes of particles mattered the most for preventing the spread of Covid-19, evidence on the effectiveness of masks did start to tip as spring turned into summer. Observational studies, models, and meta-analyses did some of the work that randomized control trials could not. The vast number of small studies of mask use against other diseases didn’t, by themselves, answer the question, but statistically tied together they came close. “The data in meta-analyses show that in those places that use masks, there was a substantial diminution of infection,” Fauci says. “Obviously it’s multifaceted, it’s more than just masks, but clearly there was a strong association.”
There still aren’t randomized, controlled trials of mask wearing against Covid-19—how would you even do that?— but some of the newer work on masks does get more specific. In June, researchers at the University of Iowa collected data on when, exactly, states with mask-wearing mandates instituted their rules. Fifteen states and Washington, DC, had done that before May 8. Then the researchers looked at those states’ subsequent growth curves in Covid-19 infections. The results were striking. Even controlling for other social-distancing measures, and without looking at how many people actually wore masks at an individual level, the curve started to bend downward as soon as a week later. Three weeks later, the daily growth rate in states with mask mandates was down 2 percent. “It’s not about the types of masks. We don’t even measure individual use of masks. We look at whether states have mandated people should use them in public and compare them before and after,” says George Wehby, a professor of health policy and management at the University of Iowa and lead author of the paper. “Many other states also had shelter-in-place laws in place, but [we still see] this effect.”
And some experimental work is at last proving the case as well. In May, a team led by Ben Cowling, an epidemiologist at the University of Hong Kong, had 246 people—all confirmed to be infected with at least one respiratory virus—exhale into a breath-collecting device called a Gesundheit-II. Half wore surgical masks and half did not. Then the team tested respiratory droplets, the air they exhaled, and took throat and nose swabs looking for viruses. The results, again, were striking. The masks stopped droplets containing influenza virus, but not aerosol particles. They did little to stop either in people infected with a rhinovirus—a cause of the common cold. But when it came to seasonal coronaviruses (not SARS-CoV-2), the masks stopped both sizes of particles. “We detected coronavirus in respiratory droplets and aerosols in 3 of 10 (30%) and 4 of 10 (40%) of the samples collected without face masks, respectively, but did not detect any virus in respiratory droplets or aerosols collected from participants wearing face masks,” the researchers wrote.
The new-ish science provides a plausible account of how public health experts changed their minds. It’s still hard not to be a little cynical about the turnabout on the part of political leaders, though. Fineberg says that the evidence hasn’t changed nearly as much as people’s attitudes toward the evidence. Some attitudes changed quicker than others. Mask wearing somehow got aligned with party affiliation—possibly because Trump himself initially refused to wear a mask, possibly because mask wearing got retroactively redefined as unmasculine, freaking out macho-aspirants.
And that was nothing compared to the local and internet-meme resistance. Even barely a week ago, Floridians were screaming at their city councils that their rules on wearing masks were part of a 5G/pedophilia conspiracy that involved “the devil’s laws.” A discredited documentary, widely spread on social media, wrongly claimed that masks actually made people sick, or cut off their air supply. Some anti-mask conservatives co-opted the rallying cry of the abortion rights movement—“my body, my choice”—to defend their anti-mask-ness. People who believe that the whole pandemic is some kind of left-wing hoax (it is not) declined to wear masks. Mask use somehow got tied up in the heady, conspiratorial brew of rugged individualism, 5G paranoia, and anti-vax sentiment. They became symbols of an insidious, freedom-sapping plot.
Some Republican leaders still say they won’t mask up. One reporter has begun naming and shaming congresspeople who don’t wear masks in the Capitol. But even that tide started to shift in early June. Maybe it was because of the preponderance of evidence. Or maybe it was because, as of June 1, when many states began “reopening” and lifting requirements on social distancing, infection numbers started declining in so-called blue states that voted for Hillary Clinton (except California) and climbing in red states that voted for Trump. It couldn’t have helped that prospective attendees at a (non-socially-distant) Trump campaign rally in Tulsa had to sign waivers saying they wouldn’t sue the campaign if they got Covid-19—and that even after the sparsely attended rally, two campaign staffers and a one-time presidential candidate who attended tested positive for the disease. Suddenly, Trump adherents knew people who were getting sick or dying.
The cultural shift to mask wearing has been gradual, more of a tide change than a tsunami. It’s hard to tell from the internet memes and broadcast news, but mask use is widely popular. According to a Pew Research study, 80 percent of Americans say they wear masks in stores or other public places at least some, if not all, of the time. Of course, just 44 percent say that most other people in their area do, which is a tell that someone is being less than candid with their pollster. Even now, nobody really knows exactly how much masks help, or which kind of mask is better than another. The deeper truth is probably, as Ristenpart says, just that “something is better than nothing.”
Rough estimates from the team that looked at state mask mandates suggest that by May 22, mask use had prevented perhaps 230,000 to 450,000 Covid-19 cases. (At an overall infection fatality rate of 1.45 percent, that’s as many as 6,500 lives saved.) Increased mask use could do it again. One modeling group at the University of Washington has gone so far as to try to quantify how many lives widespread mask wearing could save over the next few months. Last week, the Institute for Metrics and Evaluation forecast 180,000 Covid-19 deaths between now and October 1. But if 95 percent of Americans adopt mask wearing in public, their model predicts that number falls to 146,000. IHME’s models have received serious criticism for their volatility and failure to predict how slowly the US would come down from its peak of Covid-19 deaths. But IHME director Chris Murray says his team has adjusted its methods, now using new algorithms and a hybrid statistical and disease transmission model that allows for investigating the effects of different interventions, such as social distancing and mask wearing.
Based on the available evidence, his team estimates that near-universal mask wearing could cut transmission by as much as a third. Would that be enough to turn back the record-smashing tide of new cases breaking across large parts of the US? Probably, says Murray. It will depend on exactly how fast local outbreaks are growing. The reproduction number, or R0 (pronounced R-naught), is a measure of how many people one contagious person infects. If R0 is higher than 1, cases will grow exponentially. If it’s below 1, an outbreak will shrink. In places like Brazil, where a chaotic response and lack of social distancing measures has led to an R0 trending above 1.3, a mask mandate likely won’t be enough to bring cases under control. But Murray says the US still has a chance.
“Everywhere in the US right now, a one-third reduction is going to be enough to really put the brakes on most state epidemics,” he says. At the individual level, that might not seem like enough of a reduction to be worth it, but at the community level, it’s huge. “The people who were inclined to save lives are going to do it anyway,” says Murray. “If we’re trying to persuade people who are resistant to wearing a mask we should be telling them, ‘Wear a mask, save the economy.’ Because it’s a lot easier to wear a mask than be stuck at home with a stay-at-home order.”
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Adams, the surgeon general, clearly changed his tune. At a coronavirus task force briefing held on Tuesday, he said, “Please, please, please wear a face covering when you go out in public. It is not an inconvenience. It is not a suppression of your freedom. It actually is a vehicle to achieve our goals.”
In fact, some researchers are so convinced that masks—along with social distancing, staying home, and tamping down mass gatherings—are critical that they’re even recommending everyone get higher-quality surgical ones, like the ones used in hospitals, rather than fretting about which one to buy off of Etsy.
Other researchers, like Marr, are now conducting the studies necessary to tackle the complete lack of standards for homemade masks. Her lab at Virginia Tech is evaluating different materials, filters, and designs to see which ones work best. “There’s a wide range of efficacy. Bandanas barely do anything, but you can also have a good homemade mask that prevents 80 to 90 percent of particles going in both directions. But right now, there’s basically no standardization,” she says.
Such research should make it easier for people to make and buy masks that can slow the spread of SARS-CoV-2 while still preserving medical-grade masks for health care workers. Even the WHO finally came around. Spurred by the results of a review of the evidence the organization had commissioned, on June 5, the WHO announced updated guidance recommending that all citizens should wear cloth masks in areas where community transmission is ongoing.
However, WHO officials still haven’t changed their stance on not classifying SARS-CoV-2 as airborne. And until they do, it will be very difficult for governments to invest in necessary infrastructure changes—including mask manufacturing and enhanced ventilation control in buildings—to control the virus, says Morawska. “This is a lot of work, a lot of money. Why do it if the WHO is not saying airborne transmission is a problem?” she asks. To continue to put pressure on the international body, she and Donald Milton, an infectious aerosol researcher at the University of Maryland, have written an open letter entitled “It is Time to Address Airborne Transmission of Covid-19” set to be published in the journal Clinical Infectious Diseases. The commentary has been signed by 239 scientists.
In the outpouring of support, Prather sees the dam erected across the 5-micron divide starting to break. “This was never about one paper, one piece of evidence. This is about changing a whole field of view, and I think that shift is finally happening. Covid has done that,” she says. Public health officials can’t be afraid to call something airborne if it is, she says. “The sooner we acknowledge it, the sooner we can fix it.”
Without scientific clarity on Covid-19’s modes of transmission, politics and culture stepped in. As a result, where most other countries have been able to use a combination of mask wearing, testing, contact tracing, quarantines, and restrictions on mass gathering to bring the disease to heel, the United States has not. Yet those countries had the same science as the US; the difference is their leaders operated in sync with what the scientists knew rather than what the politicians hoped. Wear a mask? Yes—but not because it makes you a Lone Ranger but because, as has been true since December, we are all in this together.
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