Face shields ineffective at blocking aerosols to prevent COVID-19 spread, says study


Face shields have been seen by some as a good alternative to wearing masks, but new research shows they probably don’t do much to protect against the spread of COVID-19.

The simulation study was conducted by Riken, a research institute backed by the Japanese government, and was conducted using Fugaku, the world’s fastest supercomputer. The simulation found that nearly 100 percent of airborne droplets that are less than 5 micrometers in size escaped through a plastic visor similar to commonly worn face shields, according to the Guardian.

The simulation also found that about half of larger droplets (that were about 50 micrometers) made their way into the air.

The CDC is currently studying the effectiveness of face shields. (Reuters/Mike Blake)
The CDC is currently studying the effectiveness of face shields. (Reuters/Mike Blake)

Makoto Tsubokura, team leader at the Riken Center for Computational Science, warned against using face shields to protect against the spread of COVID-19. “Judging from the results of the simulation, unfortunately, the effectiveness of face guards in preventing droplets from spreading from an infected person’s mouth is limited compared with masks,” Tsubokura told the Guardian. That is especially true for small droplets of less than 20 micrometers, he said, but added “at the same time, it somehow works for the droplets larger than 50 micrometers.”

Currently, the Centers for Disease Control and Prevention does not recommend the use of face shields as a substitute for masks. “A face shield is primarily used for eye protection for the person wearing it,” the CDC says. “At this time, it is not known what level of protection a face shield provides to people nearby from the spray of respiratory droplets from the wearer. There is currently not enough evidence to support the effectiveness of face shields for source control.”

However, the CDC does say face shields that wrap around the sides of the wearer’s face and extend below the chin, along with hooded face shields, may provide better protection than others.

Experts aren’t surprised by the latest findings. “Face shields have been a poor alternative to masks all along,” Dr. Thomas Russo, professor and chief of infectious disease at the University at Buffalo, tells Yahoo Life. “We’ve known for a while if you wear a face shield, it doesn’t protect you from getting infected. It’s not very good at blocking respiratory particles, particularly the smaller ones.”

But Dr. William Schaffner, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells Yahoo Life that most of the methods people commonly use to prevent the spread of COVID-19 are “imperfect” on some level. “They provide some protection, but in and of itself, none of them is perfect,” he says. “Masks are the best. Face shields are good, and some face shields — those that go up high above your eyes, and down around your chin and cheeks — are better.”

What face shields can do, though, is help prevent larger respiratory droplets from splashing onto your face and going into your eyes, Dr. Raymond Casciari, a pulmonologist at St. Joseph Hospital in Orange, Calif., tells Yahoo Life. “That’s a value,” he says. “It can help prevent the spread of the virus from people who might cough, sneeze or sing, and keep those droplets from entering the ambient air around you.”

Mitchel Rosen, associate professor at the Rutgers School of Public Health and director of the Center for Public Health Workforce Development, agrees. “Face shields might reduce droplet transmission but will do little for aerosol transmission,” he says.

Aerosol transmission has been a talking point lately after the CDC published and then removed guidance that said it may be possible for COVID-19 to be transmitted through aerosols and could spread through particles that could be suspended in the air and travel more than six feet from its source. The CDC later said that the guidance was posted in error.

It’s important to keep in mind, though, that this research is via simulation and not a clinical trial with people that resulted in infections, Dr. Amesh A. Adalja, senior scholar at the Johns Hopkins Center for Health Security, tells Yahoo Life. “Face shields are obviously not going to trap aerosols, based on their design. But the question is, are those aerosols important for people getting infected?” he says. “Even a homemade mask or surgical mask isn’t going to stop aerosol droplets. But are people getting infected this way? That’s the question.”

The CDC is currently studying the effectiveness of face shields, and that may provide data on “how important it is to block every aerosol,” Adalja says.

Until then, Schaffner recommends that people who like to wear a face shield pair it with a mask. “It’s the current standard to protect health care workers,” he says. “If you do both, you have a second layer of protection. Each one is good, but together they’re better.”

For the latest coronavirus news and updates, follow along at https://news.yahoo.com/coronavirus. According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.

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