Welcome to the second part of our special series that investigates how well face shields work as coronavirus protection. In our previous entry, we explored what happens when someone who might be carrying COVID-19 is wearing a face shield. Did you miss it? Check it out here.
For this article, we'll take a look at the other end of the equation — do face shields protect wearers from COVID-19 carriers?
Are Face Shields Good Coronavirus Protection for the Wearer?
The scientific evidence surrounding face shield effectiveness is mixed. On the bright side, a recent study by the Israel Institute for Biological Research found they were just as effective as a face mask when a wearer is directly coughed or sneezed at from 2 feet away. The visors also protect the eyes, which can be an entry point for many viral infections. Lastly, some researchers think they reduce the risk of people inadvertently touching their faces and inoculating themselves with a virus.
These are all valid points to consider. But the reality is that face shields only perform well under ideal conditions, such as the study mentioned above. In truth, face shield wearers often have to move around in close proximity to others. That's where things get tricky.
The Israel Institute for Biological Research simulated this more realistic situation; they moved the "cough source" 1 foot above and below the face shield. Droplets quickly circulated around the visor's edges and covered the shield wearer's face (in this experiment, a mannequin). The conclusion of this study? Face shields only blocked droplets with a 45% success rate.
Why Aerosols Are Important to Consider
Research tests usually don't use virus-containing aerosols. But the US National Institute for Occupational Safety and Health ran one involving face shields and the influenza virus. Similar to the Israel Institute for Biological Research's results, they found that face shields only blocked 68% of smaller aerosols.
When considering the fact that the fine mists of aerosols we all release when talking, singing, coughing, or sneezing don't just disappear — they linger in the air — this is extremely worrisome. Larger droplets tend to fall to the ground or onto other surfaces. But the smaller particles can hang around in the air for several minutes or even a couple of hours in indoor environments.
It's important to note that well-ventilated rooms do substantially decrease the time these aerosols linger in the air. But there have been reports of coronavirus-contaminated droplets making their way into building ventilation systems: a Singapore hospital treating COVID-19 patients had its air exhaust outlets swabbed and tested. The results came back positive.
The tests by the US National Institute for Occupational Safety and Health showed it only takes 30 minutes for aerosols from a cough to spread throughout a room. Since these microdroplets can easily creep around the sides of plastic visors, it's no surprise that researchers found that face shields reduced the inhalation of these infected aerosols by only 23%.
It's still not completely clear how many COVID-19 virus copies can be transmitted through aerosols. Flu research shows that tens of thousands of influenza virus copies can linger in these airborne droplets. And recent research suggests that the smaller droplets can linger in the air for up to 3 hours.
Still Wearing a Face Shield? Wear a Face Mask Underneath It
Many researchers have said that if you're going to don a face shield, you should also wear a face mask underneath it for optimal COVID-19 protection. From the studies mentioned above, it's clear that a face shield alone is not very protective when accounting for real-world conditions.
Ideally, the face mask protection option you choose should fit snugly around your nose to minimize any gaps in which aerosols can enter or escape. It should also be thick or multi-layered. Also, when indoors, stick to well-ventilated rooms. And, of course, maintain six feet of social distance from other people as much as possible.
There's no telling when the COVID-19 pandemic will end. Some research suggests that it could take as long as the end of 2021 for a proper vaccine to be created. Until then, it's always better to be safe than sorry as this crisis plays out.
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