SELF - Are Face Shields Even Better Than Face Masks at Preventing Coronavirus Infection?
If you wear a face mask when you leave your home, you’re probably not doing it because you want to. Masks are awkward and uncomfortable, and they can be difficult to use correctly: If they aren’t applied and removed with clean hands, they can actually transmit infection rather than prevent it.
A growing number of researchers think there’s a better way. Face shields—which shield a person’s face with a clear curved plastic panel—are more comfortable, easier to put on and take off, reusable, and simple to clean. But most importantly, “we feel face shields are far more effective,” Eli Perencevich, M.D., a professor of internal medicine and epidemiology at the University of Iowa Carver College of Medicine, who in April published a commentary in JAMA in favor of face shields with two of his colleagues, tells SELF.
Research on face shields is limited but promising. In a 2014 Journal of Occupational and Environmental Hygiene study, researchers at the National Institute for Occupational Safety and Health placed a face shield on a breathing robot and had another robot 18 inches away “cough out” flu virus. The shield prevented the breathing robot from inhaling 96 percent of the virus within five minutes. In additional tests, the shield’s effectiveness varied based on the size of droplets expelled, but the overall indication was that shields can protect their wearers from other people’s germs.
No studies have yet addressed whether face shields protect other people from your germs, however, and this makes some scientists wary. “We don’t have the research to say that they will offer protection for those around you, should you be sick,” Saskia Popescu, Ph.D., an infection prevention epidemiologist at George Mason University, tells SELF.
But face shield proponents argue that based on the laws of physics, shields will likely protect others. Everything that flies out of your mouth is “going forward, and it’s hitting a giant piece of plastic,” Dr. Perencevich says. “It just physically can’t go through.”
Dr. Perencevich and others are now designing studies to help address this issue, but he says it’s difficult for research like this to get funded. “We’re more interested as a society in treatment than we are in prevention,” Michael Edmond, M.D., a hospital epidemiologist at the University of Iowa Carver College of Medicine, who co-authored the JAMA commentary with Dr. Perencevich, tells SELF. “There’s never money to do this kind of work. It’s never been prioritized.”
Some people are skeptical of shields because they are open on the sides and bottom. But these openings may not pose much of a problem. Research suggests that the coronavirus usually spreads via large droplets expelled out of a person’s mouth or nose, which are pulled down by gravity within a radius of six feet. (Hence the six-foot rule.) Shields prevent close-by expelled viruses from hitting another person’s face before they fall.
To get in through the shield’s openings, the virus would need to linger around in the air in smaller particles known as aerosols and eventually meander around the shield’s sides. But “the patterns of spread of [COVID-19] suggest that aerosol is unusual,” David Fisman, M.D., an infectious disease epidemiologist at the University of Toronto, tells SELF. Some studies have found that the virus can linger in the air, but epidemiological findings—such as surprising data suggesting that people often do not get sick even when other members of their household have the coronavirus—suggest that aerosol transmission is uncommon.
Still, for those who are concerned about the potential role of aerosols, or who might be at high-risk for complications from the coronavirus, one solution might be to wear shields and masks at the same time, suggests William Lindsley, Ph.D., a bioengineer with the National Institute for Occupational Safety and Health, who co-authored the 2014 robot coughing study. When robots wore both shields and masks in his study, the shields blocked 97 percent of the virus from landing on the masks, keeping them much cleaner.