Should we wear masks? The science shaping a pivotal debate, explained

There are now over 190,000 cases of Covid-19 in the United States. As the pandemic continues, we may be on the brink of a large shift in the way we think about containing the virus, and protecting ourselves from infection.

At the center of this shift is the humble, yet powerful and increasingly scarce, face mask.

According to internal United States Centers for Disease Control and Prevention documents obtained by the Washington Post on Wednesday, the agency is considering cloth-based masks to reduce virus transmission, and may recommend that the American public wear such masks outside their homes.

But what scientific evidence is there that we should mask up, or not? The waters are murky, to say the least.

At the time of writing, the CDC's current policy surrounding masks has not changed. Face masks are not considered necessary for use among the general public unless you are symptomatic, or are caring for someone who is.

The World Health Organization doubled down on this line of thinking on Monday.

That said, a lot of official policy around coronavirus has changed significantly in the past few weeks. And there are signals that we may soon see a sea change in mask policy in the United States.

On Monday, March 30, CDC director Robert Redfield told NPR that the data on whether masks may prevent the spread of Covid-19 is being "aggressively reviewed as we speak." National Institute of Allergy and Infectious Diseases director Anthony Fauci has also hinted the idea is under serious consideration at the top levels of government

But while we await the official word on whether to mask or not, a furious debate around their efficacy has emerged among the scientific and lay communities.

Medical-grade masks are still a scarcity in some hospitals, driving clinicians and other healthcare providers to ration them, make their own, or call for donations. The debate over whether regular people should now wear masks, meanwhile, has a crucial caveat: If people are to wear masks outside of specific settings that call for medical-grade supplies, they would likely be cloth masks. These are not medical-grade personal protective equipment (PPE), like N95 respirators ("A scarf would be very good" as President Trump noted) .

Already, clinicians and people coming into contact with the healthcare system in the United States are seeing significant changes in the way masks are distributed. Major medical institutions, like Massachusetts General Hospital are adopting universal masking policies, under which everyone at a hospital (visitors, janitorial staff, doctors) are given a mask to wear upon entry.

"You don't need a fancy mask, you can use a homemade mask or a bandana."

Peter Chin-Hong is an infectious disease specialist at the University of California San Francisco. Their hospital has the same policy in place. Although the mask debate might affect PPE shortages, he tells Inverse that there is a time and a place for certain members of the public to consider wearing a mask.

"The virus doesn’t care if you’re a visitor, if you’re staff, if you’re a delivery person," he says.

"When the disease prevalence is low in a population, it probably doesn’t matter if you use a mask or not. But as disease prevalence increases and chances of a random person coming by you becomes higher, protection – the mask – becomes more important."

What changed?

SARS-Cov-2 is transmitted via droplets that emerge from your body when an infected person coughs or sneezes (Chin-Hong calls the nose and mouth "paradise" to the virus). And there are signs that the virus is being transmitted among people who may not otherwise feel sick.

In a letter published in the New England Journal of Medicine, researchers analyzed 17 patients and found that one asymptomatic patient had a similar viral load to the other symptomatic patients, suggesting that asymptomatic people can spread the virus.

In the NPR interview, Redfield suggested that as many as 25 percent of cases may spread this way.

"I’ve seen hundreds of infections," Chin-Hong says. "This infection occurs and spreads before you feel sick. Coupled with the fact that we don’t have enough testing in the United States, it leads to a bad situation."

The risk of asymptomatic transmission may be an argument for mask wearing, he says.

"It would be irrational if we do not consider the mask as a complementary tool."

But so far, the published science regarding the utility of masks has been inconsistent, at best.

A 2012 review paper detailing 17 clinical trials found none of them established a conclusive link between mask use and protection from the flu. But they may be useful if used in tandem with other hygiene habits, the authors concluded. That conclusion jibes with a 2011 review of 67 studies on respiratory viruses, which suggested that masks are an effective way to slow the spread of such viruses.

For now, Chin-Hong says there are benefits to covering your nose and mouth, but they are greater in certain scenarios than others.

For instance, if you live in rural areas and are easily able to maintain 6 feet of distance from people, you may get as much or more protection from social distancing as you would from wearing a mask, he says.

But if you live in a hotspot or cannot reasonably maintain that crucial 6 feet of distance, like in New York City, for example, masks may be more useful. Imagine a New York subway, or a grocery store worker who has to encounter hundreds of strangers each day in close quarters, he says.

"Not everyone needs to wear a mask all the time," he says. "If you can't control your environment it really is important for people in the community to protect themselves. You don't need a fancy mask, you can use a homemade mask or a bandana."

Elaine Shuo Feng is an epidemiologist at the University of Oxford's Vaccine Group. She agrees that not everyone needs a mask. Rather, she suggests the following people consider mask usage:

1. High-risk groups, like the elderly, or people with underlying health conditions.
2. People who have confirmed Covid-19, or who are showing symptoms.
3. People exposed to Covid-19.

For the general public, she says masks "would be helpful in flattening the curve."

But we still need to consider that such a policy take masks away from medical workers when supplies are limited.

"Precautious [are] needed to preserve N95 and surgical masks for healthcare workers. [For the general public] Self-made masks might be helpful, but further guidelines [are] needed," she tells Inverse.

For the rest of us, Chin-Hong points out that, should we move towards more universal mask usage, it is not an excuse to stop social distancing. Nor are they an excuse to touch your face.

Masks can used in addition to other good hygiene habits, but not as a replacement for them.

"Summarizing from scientific evidence, face masks might not have a large effect."

No panacea

Some scientists are quite outspoken about the use of masks. Chi-chiu Leung is chairman of the Hong Kong Medical Association's Advisory Committee on Communicable Diseases. In Hong Kong, wearing face masks in common.

He is also the author of a letter advocating for mask-use in The Lancet.

"To us, it would be irrational if we do not consider the mask as a complementary tool for such unavoidable contacts," he tells Inverse.

"Only by an ALL-OUT strike to rapidly suppress the community transmission, like what happened in China, can we resume essential parts of our economy before all our response capacity, stock and supplies are exhausted."

But even those who support mask-wearing don't claim it will solve every problem ahead of us – especially the supply issues.

Even Hong Kong struggled with mask shortages and skyrocketing prices in early February, asThe Hong Kong Free Press reported.

Feng also cautions that masks are not the panacea they may be portrayed to be, but at this point, anything helps.

"Summarizing from scientific evidence, face masks might not have a large effect, but even it works a bit to reduce the disease transmission, it could help a lot in terms of number of infection averted, given it is such a cheap intervention compared to others," she says.

Two truths can exist at the same time. Masks may have shown inconsistent results in clinical trials demonstrating their efficacy. Scientists, though, suggest the benefits of masks still exist, and wearing them outside may be worth considering as the pandemic continues.

But no matter where the mask debate leads, keeping medical-grade masks in the hands of those who need them most, is the top priority, Feng says.

At the same time, people need guidelines to empower them to make their own, she says.

"Governments may need to ramp up the manufacturing capacity, or importation, or provide guidelines on DIY masks for the public," she says.