Far-UVC light efficiently and safely inactivates airborne human coronaviruses

Abstract

The global spread of coronavirus disease (COVID-19) has escalated the need for public sanitation. Ultraviolet (UV) light is a well-established antimicrobial; however, the UV light commonly used for this purpose (~254 nm) poses significant health risks in public spaces due to its cancer-causing effects. Far-UVC light (~207-222 nm) has similar germicidal properties without health risks, as it does not penetrate human eye or skin cells. This group previously found low doses of far-UVC light (222 nm) to be an effective germicide against aerosolized H1N1 influenza virus. In this study, the researchers tested two viruses that are closely related to SARS-CoV-2, the virus that causes COVID-19. Because the sensitivity of a virus to UV is determined by its genome size and all coronaviruses have genomes of similar sizes, it is reasonable to expect the sensitivity of SARS-CoV-2 to be comparable to these viruses.The authors tested several doses of far-UVC on aerosolized viruses. They found that for both viruses tested, 99.9% of the virus was inactivated at a lower dose than the one needed to inactivate H1N1 virus. The authors also suggested a safe dose for an 8-hour work shift based on recommendations from the International Commission on Non-Ionizing Radiation Protection (ICNIRP). At this dose, 90% of aerosolized viruses would be deactivated in 8 minutes, 95% in 16 minutes, and 99% in 25 minutes. These results combined with the earlier results for H1N1 suggest that low doses of far-UVC light in heavily occupied spaces would reduce the spread of viral diseases, likely including COVID-19.

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A direct approach to limit airborne transmission of pathogens is to inactivate them within a short time of their production. Germicidal ultraviolet light (UV), typically at 254 nm, is effective in this context, but it is a health hazard to the skin and eyes. By contrast, far-UVC light (207-222 nm) efficiently kills pathogens without harm to exposed human cells or tissues. We previously demonstrated that 222-nm UV light efficiently kills airborne influenza virus (H1N1); here we extend the far-UVC studies to explore efficacy against human coronaviruses from subgroups alpha (HCoV-229E) and beta (HCoV-OC43). We found that low doses of, respectively 1.7 and 1.2 mJ/cm2 inactivated 99.9% of aerosolized alpha coronavirus 229E and beta coronavirus OC43. Based on these results for the beta HCoV-OC43 coronavirus, continuous far-UVC exposure in public locations at the currently recommended exposure limit (3 mJ/cm2/hour) would result in 99.9% viral inactivation in ~ 25 minutes. Increasing the far- UVC intensity by, say, a factor of 2 would halve these disinfection times, while still maintaining safety. As all human coronaviruses have similar genomic size, a key determinant of radiation sensitivity, it is realistic to expect that far-UVC light will show comparable inactivation efficiency against other human coronaviruses, including SARS-CoV-2.

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