In a past study, this research group was the first in the world to demonstrate that a unit with Ushio’s Care222 light technology inactivates the original strain of SARS-CoV-21) and that the inactivation effect of UV-C light with a central wavelength of 222 nm on SARS-CoV-2 depends on cumulative illuminance regardless of lighting method (continuous, intermittent, etc.).2) The group also reported that 222 nm UV-C light would inactivate N501Y variants as effectively as it inactivates the original SARS-CoV-2 strain.3)
COVID-19 infections are currently increasing due to multiple variants of SARS-SoV-2. According to an internal document from the U.S. Center for Disease Control, the basic reproduction number (R0) indicating how many people a single patient may infect ranged between two and three for the original strains, whereas it ranged between five and nine for the Delta variant, the same level as the chickenpox.4) The hospitalization rate of patients with the Delta variants is reported to be double the hospitalization rate of patients with the Alpha variant.5) Further, laboratory testing revealed that the Delta variant has greater resistance to neutralizing antibodies compared to the original strain of the virus, even in patients who have received two doses of a vaccine. This suggests a possible decrease in the vaccine’s efficacy.6) At the same time, it is believed to be possible to predict the amount of UV-C light needed to inactivate the virus.7) The SARS-CoV-2 variants have mutations in some parts of the genome that occur during copying and proliferation that do not significantly affect the genome size or base composition that determines sensitivity to UV-C light.8) As such, researchers speculated that sensitivity to inactivation by 222 nm UV-C should not differ between the original strains and variants. The researchers had already shown that irradiation with 222 nm light inactivated the N501Y variants as effectively as it inactivated the original strain, as initially believed. The next step was to evaluate the effect of 222 nm UV-C light in inactivating the Delta variant.
Therefore, Ushio conducted a joint research project with researchers from Hiroshima University Hospital’s Department of Infectious Diseases and the Virology Department of Hiroshima University’s Graduate School of Biomedical and Health Sciences to verify that irradiation with UV-C light with 222 nm wavelength would inactivate the Delta variant equally effectively.