UV Sterilization: Far-UVC light kills airborne flu viruses without danger to humans

Use of overhead far-ultraviolet C light in public spaces could provide a powerful check on seasonal influenza epidemics, as well as influenza pandemics.

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Continuous low doses of far-ultraviolet C (far-UVC) light can kill airborne flu viruses without harming human tissues, according to a new study at the Center for Radiological Research at Columbia University Irving Medical Center (New York, NY).1 The findings suggest that use of overhead far-UVC light in hospitals, doctors’ offices, schools, airports, airplanes, and other public spaces could provide a powerful check on seasonal influenza epidemics, as well as influenza pandemics.

Scientists have known for decades that broad-spectrum UVC light, which has a wavelength between 200 and 400 nm, is highly effective at killing bacteria and viruses by destroying the molecular bonds that hold their DNA together. This conventional UV light is routinely used to decontaminate surgical equipment. “Unfortunately, conventional germicidal UV light is also a human health hazard and can lead to skin cancer and cataracts, which prevents its use in public spaces,” says study leader David Brenner.

Several years ago, Brenner and his colleagues hypothesized that far-UVC could kill microbes without damaging healthy tissue. “Far-UVC light has a very limited range and cannot penetrate through the outer dead-cell layer of human skin or the tear layer in the eye, so it’s not a human health hazard. But because viruses and bacteria are much smaller than human cells, far-UVC light can reach their DNA and kill them,” Brenner said.

Excimer lamp sources

Brenner and his group use filtered excimer lamps emitting in the 207–222 nm wavelength range (see figure). For example, 207 nm light is emitted by a krypton-bromine excimer lamp, while 222 nm is emitted by a krypton-chlorine excimer lamp. Brenner’s group started with the 207 nm lamp, publishing results on sterilization of bacteria in 20132—in 2017, the results at 222 nm for bacteria were reported.3

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Antiviral effectiveness of 222 nm far-UVC light produced by an excimer lamp (inset) is shown in terms of fractional survival as a function of dose; the means and standard deviation for each dose are shown in blue.

The latest study showed that far-UVC at 222 nm inactivates more than 95% of airborne aerosolized H1N1 influenza viruses at a low dose of 2 mJ/cm2. Because light at wavelengths from 207 to 222 nm are completely absorbed by the dead outer layer of skin and by the outer tear layer of the eye, these wavelengths are safe for humans (unlike the commonly used 254 nm germicidal wavelength that can cause skin cancers, including deadly melanoma).

As a result, continuous very low-dose-rate far-UVC light could be integrated into overhead lamps for hospitals, schools, airports, and so on—potentially drastically reducing influenza. As a bonus, UVC light could prevent the spread of airborne microbial diseases such as tuberculosis.

While the use of UV germicidal irradiation to kill germs is not new, the use of conventional (not far) UVC requires some way of greatly limiting peoples’ light exposure, such as the addition of louvers to prevent direct exposure to UV. These setups intrinsically are more limited in their usefulness, as they don’t irradiate the entire room. In contrast, use of low-level far-UVC fixtures safely irradiate areas full of humans and their clouds of viruses.

At a price of less than $1000 per lamp, a cost that would likely decrease if the lamps were mass-produced, far-UVC lights are relatively inexpensive. “And unlike flu vaccines, far-UVC is likely to be effective against all airborne microbes, even newly emerging strains,” Brenner says.

REFERENCES

1. D. Welch et al., Sci. Rep. (2018); doi:10.1038/s41598-018-21058-w.

2. M. Buonanno et al., PLOS One (2013); see https://goo.gl/MqJT5V.

3. M. Buonanno et al., Radiat. Res. (2017); see https://doi.org/10.1667/rr0010cc.1.

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