As students return to school, are face shields really effective against COVID-19?

Face masks are OK to wear to protect against COVID-19, right? Wrong.

That’s according to latest experiment on the subject showing how droplets spread while wearing a face shield and a face mask with exhale valves compared to droplets from a traditional mask. College and high-school students and children in elementary schools are returning to classes this week — and some are wearing face shields with a cloth mask, and sometimes without one.

The Orange County Health Care Agency, the Orange County Department of Education and school districts across that county, for instance, have developed a guide to returning to school. It says face coverings are strongly encouraged for young children between two years old and second grade: “A face shield is an acceptable alternative for children in this cohort who cannot wear them properly.”



‘No burden of 100% efficacy should be placed on face shields or any containment policy because this level of control is both impossible to achieve.’

— A commentary published by JAMA Network, an open-access medical journal published by the American Medical Association

Vanderbilt University in Nashville, Tenn., among some other colleges, recommends faculty members within classrooms should wear a face shield without a mask. But research suggests that may not be enough to prevent a teacher wearing the mask from spreading coronavirus, especially if he/she is asymptomatic or pre-symptomatic. (Vanderbilt did not return request for comment.)

To reduce the risk of spreading COVID-19, the disease caused by SARS-CoV-2, it may be preferable to use high-quality cloth or surgical masks that are of a plain design instead of face shields and masks equipped with exhale valves, according to an experiment published Wednesday by Physics of Fluids, a monthly peer-reviewed scientific journal covering fluid dynamics.

The journal, which was first established by the American Institute of Physics in 1958, published the study, “Visualizing droplet dispersal for face shields and masks with exhalation valves,” to illustrate how the movement of droplets compared to wearing a face mask without valves. Their conclusion: It may be preferable to use high-quality cloth or surgical masks with plain design without valves.

“We focused on the smaller droplets, since they can stay suspended for very long times and might contain enough virus particles to transmit COVID-19,” said Siddhartha Verma, assistant professor at the Department of Ocean and Mechanical Engineering at Florida Atlantic University in Boca Raton, Fla. “Even the very best masks have some degree of leakage.” (Watch the video here.)

Face shields block the initial forward motion of a simulated jet of a cough or a sneeze, but the expelled droplets can move around the visor with relative ease and spread out over a large area, the experiment concluded. The experiment also suggested that droplets can pass through an exhale valve unfiltered. “which significantly reduces its effectiveness as a means of source control.”

This experiment published by Physics of Fluids, a peer-reviewed scientific journal, looks at droplet spread from face shields and face masks with exhale valves, and compares them to those of traditional cloth face masks. (Image courtesy of: Siddhartha Verma, Manhar Dhanak and John Frankenfield)

“As students return to schools and universities, some have wondered if it is better to use face shields, as they are more comfortable and easier to wear for longer periods of time,” said Verma. “But what if these shields are not as effective? You would be essentially putting everyone in a tight space with droplets accumulating over time, which could potentially lead to infections.”

Other universities won’t admit students without a mask and shield. The Centers for Disease Control and Prevention does not recommend face shields as a substitute for masks: “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.”

‘What if these shields are not as effective? You would be essentially putting everyone in a tight space with droplets accumulating over time.’

— Siddhartha Verma, assistant professor at the Department of Ocean and Mechanical Engineering at Florida Atlantic University

The CDC reminds people to distinguish between masks, and surgical masks. “Currently, those are critical supplies that should continue to be reserved for health-care workers and other medical first responders,” it says. “Masks also are not appropriate substitutes for them in workplaces where surgical masks or respirators are recommended or required and available.”

While face shields and masks with valves may be more comfortable than cloth masks, the CDC calls for wearing a mask that covers both your nose and your mouth, with the mask secured under your chin. It should fit snugly against your face. There should not be large openings or gaps around your nose, mouth and the sides of your face. Do not touch the mask while wearing it.

Some educational institutions are equally circumspect on the use of face shields. Loma Linda University, a Seventh-day Adventist health-sciences university in California, advises the wearing of face masks as the No. 1 protection against COVID-19. “Prolonged exposure reduces the amount of protection of the shield,” according to this advice on the university’s health and wellness team.

Vanderbilt University’s Public Health Advisory Task Force, in a statement on the college’s website, cited a “preliminary study” as offering sufficient evidence for the efficacy of face shields. However, that preliminary study is actually “viewpoint” commentary on face shields that cites other pieces of research on face shields and the influenza virus, which is obviously different from coronaviruses.

That commentary published by the JAMA Network concludes: “It is unlikely that a randomized trial of face shields could be completed in time to verify efficacy. No burden of 100% efficacy should be placed on face shields or any containment policy because this level of control is both impossible to achieve and unnecessary to drive SARS-CoV-2 infection levels into a manageable range.”

Coronavirus update

As of Wednesday, COVID-19 has infected 25,785,890 people worldwide, which mostly does not account for asymptomatic cases, and killed 857,821. The U.S. still has the world’s highest number of COVID-19 cases (6,076,425), followed by Brazil (3,950,931), India (3,769,523) and Russia (1,001,965), according to data aggregated by Johns Hopkins University.

In the meantime, cases keep rising in the U.S. with California becoming the first state in the country to surpass 700,000 confirmed cases; infections hit 715,617 there as of Wednesday with 13,150 COVID-related deaths. New York has recorded 435,510 infections and the highest number of deaths in the U.S. (32,966). COVID has killed 184,697 people in the U.S.

AstraZeneca AZN, +0.10% , in combination with Oxford University; BioNTech SE BNTX, +3.00% and partner Pfizer PFE, +0.82% ; GlaxoSmithKline GSK, +1.82% ; Johnson & Johnson JNJ, +1.15% ; Merck & Co. MERK, -0.62% ; Moderna MRNA, -2.06% ; and Sanofi SAN, -2.27% are among those currently working toward COVID-19 vaccines.

The Dow Jones Industrial Index DJIA, +0.70%, the S&P 500 SPX, +0.57% and the Nasdaq Composite COMP, -0.15% were all trading higher on Wednesday. Over the past five months, the Dow’s advanced 31%, its biggest 5-month percent gain since July 2009, while the S&P 500 added over 36%, its best 5-month run since October 1938.


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