Omicron is the most infectious variant of SARS-CoV-2 to date, sending COVID-19 infection rates around the world to record-breaking heights and leaving many searching for supplemental ways to protect themselves.
As to why omicron is so transmissible, science has yet to find a definitive answer aside from its ability to evade immunity. As Nature recently reported, the viral load— which is the amount of virus that builds up in someone's body — in people infected with delta appears to be slightly higher than those with omicron. Omicron's rapid spread could also be a result of Americans, particularly in states with few protective measures, going about their lives unmasked after testing positive with omicron.
Common means of reducing transmission include social distancing, sanitization, and mandating masks of varying degrees of filtration. These protective measures all rely on the principle that the SARS-CoV-2 virus is spreading through the mouth and nasal passages.
Yet what if COVID-19 were spreading in other ways?
This is the hypothesis that was partially tested by a study published in the Cambridge University Press journal Infection Control & Hospital Epidemiology, in which researchers tested the effectiveness of a "multimodal" preventative measure policy implemented in long-term care facilities. This included having employees of these care facilities universally don face-shields, in addition to masks. The personal protective equipment policy was successful, and the long-term care facilities reported "no cases within 20 nursing home units over the first 6 months of the pandemic."
Because this study was performed with multiple modes of protection, it is hard to single out the singular effect of the face shields within the mix of protective gear.
"We have demonstrated that proactive and comprehensive strategies, including universal face shield and face mask, can effectively prevent COVID-19 outbreaks in [long-term care facilities] in regions with high-levels of community transmission even without universal testing," the researchers stated.
Indeed, if face shields do slightly lower COVID transmission, the reason could be related to the potential for the virus to spread through infection via the eye. That infection could come about in one of two ways: through contact with infected air particles, or through rubbing one's eye.
Scientists know that COVID-19 generally spreads by breathing in air when one is in close proximity to an infected person. In the standard transmission model, a person inhales small particles, known as virions, from the infected person. These virions contain the virus. Once the virions enter a person's body, the virus' spike protein facilitates the transfer of the virus' contents into one's cells. The virus eventually binds to a specific receptor, known as the ACE2 receptor, which leads to an infection.
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"The ACE2 receptor is present all over your body, and of course, then, when the virus encounters a cell with that receptor, it can get inside and reproduce and infect other cells in your body," said John Volckens, an aerosol scientist and professor in the Colorado School of Public Health at Colorado State University (CSU).
Still, Volckens was somewhat skeptical that the virus might get in via one's eyes.
"Yes, your eye does have these two receptors, so it is possible to get infected by SARS-CoV-2 through your eyes — but I would say it's unlikely," he noted.
But why? Volckens said it's a numbers game, and that it is simply much easier for the virus to infect via one's lungs.
He compared the area of different organs for infection. "The surface area of your eye is about the size of your thumb, if you open your eye wide, but not much bigger than that," he said, whereas, "the surface area of your lungs is the size of a tennis court."
"Furthermore, you're constantly cycling air over the surface of your lungs, so if you breathe about 10 cubic meters of air, enough air to fill up a small kitchen per day, that's a huge amount of air to cycle over a huge surface area — unlike your eyes," he added.
Volckens said from a "dimensional standpoint," the lungs represent a larger site of infection than your eyes, which is why he said it is less likely — though not impossible — to get an infection vis-a-vis one's eyes.
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Yet there is one more likely route of eye infection of COVID-19: if one were to touch an infected surface and rub their eyes, that might result in infection.
"There have been suspected cases of eye infection for SARS-CoV-2, and most of those reports suggest eye touching — not someone sneezing in your eye," Volckens said. "Yes, I mean if someone was really sick and infectious with SARS-CoV-2 and they sneezed in your face, you bet you'd get infected through your eyes, but that just doesn't happen very often, so it's less likely — what's more likely is that someone sneezes in the room near you and you inhale that air."
Volckens said he would still recommend face shields for those who are in frequent contact with people face-to-face — say, a bank teller, or someone who works with high-risk individuals who cannot be masked for some reason.
"Somewhere where you're indoors and you're taking orders at a restaurant, like a fast food restaurant, where you're two or three feet from 1,000 strangers per day, and they're all talking at you right within six feet, and they're all unmasked — if all those things are true I could see a face shield being a helpful source of personal protective equipment," Volckens said. "But if you are indoors and people are masked, and you're in a mask, face shields are not going to do much for you."
Researchers believe that the omicron variant is highly transmissible — about 2.7 to 3.7 times more infectious than delta in vaccinated, boosted people and unvaccinated people. So could a small measure, like wearing a face shield, have a minute effect on lowering transmissibility?
"You might see more eye infections [with omicron], but we're talking like one in a 10,000 to two in 10,000 infections — whereas the other nine 9,998 are more likely to happen through airborne transmission or through surface transmission where you touch something and infect yourself," Volckens estimated.
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