Welcome to the second entry of our special series that explores the efficacy of face shields as coronavirus protection. In our previous post, we investigated what happens when someone who might be carrying COVID-19 is wearing a face shield. If you missed it, you can check it out here.
For this final chapter, we'll look at the other end of the equation — do face shields protect wearers from COVID-19 carriers? Let's dive right in.
Do Face Shields Fare Well as Coronavirus Protection for the Wearer?
The scientific evidence surrounding face shield effectiveness is mixed. For example, a recent study by the Israel Institute for Biological Research found that 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 believe that they reduce the risk of people touching their faces and inadvertently inoculating themselves with a virus.
These are all valid points to consider. But the truth is that face shields seem to perform best under ideal conditions. For instance, when someone is coughing directly onto the plastic surface of the visor, as was done in the study mentioned above. In reality, face shield wearers often have to move around in close proximity to others. And this is where things get tricky.
The Israel Institute for Biological Research tried to simulate this more common situation; they moved the "cough source" 1 foot above and below the face shield. The face of the shield wearer (in this case, a mannequin) quickly became covered with droplets that circulated around the visor's sides. The researchers concluded that face shields were only blocked droplets with a 45% success rate.
Why Aerosols Are Such a Big Deal
Research tests that use aerosols actually containing a virus are few and far between. 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 blocked 96% of large airborne viral droplets. But it only blocked 68% of smaller aerosols.
This is extremely worrisome when you consider that the fine mists of aerosols we all release when talking, singing, coughing, or sneezing don't just disappear — they linger in the air. While the larger droplets do fall to the ground or onto other surfaces, the smaller particles we produce can hang around in the air for several minutes or even a few hours in some indoor environments.
It's important to note that the time these aerosols linger in the air decreases substantially for well-ventilated rooms. But there have been reports of coronavirus-contaminated droplets making their way into building ventilation systems. For example, 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 that aerosols from a cough can spread throughout a room in just 30 minutes. Considering the ease with which these microdroplets can 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.
If You Wear a Face Shield, Wear a Face Mask Underneath It
The majority of researchers agree that if you're going to wear a face shield, you should also wear a face mask underneath it for optimal COVID-19 protection. All studies indicate 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. This minimizes any gaps in which aerosols can enter or escape. It should also be thick or multi-layered. Also, stick to well-ventilated rooms when indoors. And, of course, maintain six feet of social distance from other people as much as possible.
There's no telling how long the COVID-19 pandemic will go on for. Some research suggests that it could take as long as until 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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