Safer UV light can effectively kill coronavirus without harming humans, say scientists

Scientists have shown for the first time that a form of ultraviolet (UV) radiation, which is safer to use around humans, can effectively kill the novel coronavirus that causes Covid-19, an advance that may lead to a potent disinfection system for occupied public spaces including hospitals.

The study, published in the American Journal of Infection Control, offers first proof that Ultraviolet-C (UVC) light with a wavelength of 222 nanometeres (nm) effectively kills the SARS-CoV-2 virus, and it may not penetrate the human skin.

According to the researchers, including those from Hiroshima University in Japan, previous studies involving 222 nm UVC, also known as Far-UVC, have so far only looked at its potency in eradicating seasonal coronaviruses that are structurally similar to the novel coronavirus, but not on SARS-CoV-2 itself.

"Recent studies have shown that 222-nm UVC is less harmful than 254-nm UVC because far-UVC light has a very limited penetration depth in the skin or eyes, and it is also an efficient anti-microbial technology," the scientists wrote in the study.

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In the current research, the researchers spread a 100 microliter solution containing the virus onto a nine-centimeter sterile polystyrene plate, and allowed it to dry in a biosafety cabinet at room temperature before placing the Far-UVC lamp 24 centimeters above the surface of the plates.

They showed that 99.7 per cent of the SARS-CoV-2 viral culture was killed after a 30-second exposure to 222 nm UVC irradiation.

The study noted that at this wavelength of 222 nm, UVC cannot penetrate the outer, non-living layer of the human eye and skin.

So the scientists said the radiation would not cause harm to the living cells beneath.

According to the researchers, this makes the light safer, but also an equally potent alternative to the more damaging 254 nm UVC germicidal lamps increasingly used in disinfecting healthcare facilities.

Since 254 nm UVC harms exposed human tissues, they said it can only be used to sanitise empty rooms.

But the 222 nm UVC can be a promising disinfection system for occupied public spaces including healthcare facilities where hospital-bourne infections are a possibility, the scientists noted.

Citing the limitation of the study, the researchers said they only investigated the efficacy of 222 nm UVC in lab conditions.

"We did not evaluate this technology in a real-world setting, such as a surface counter-top," the scientists noted.

They suggested further evaluation of the safety and effectiveness of 222 nm UVC irradiation in killing SARS-CoV-2 viruses in real-world surfaces.