SARS-CoV-2 disinfection in aqueous solution by UV₂₂₂ from a krypton chlorine excilamp

There is an urgent need for evidence-based development and implementation of engineering controls to reduce transmission of SARS-CoV-2, the etiological agent of COVID-19. Ultraviolet (UV) light can inactivate coronaviruses, but the practicality of UV light as an engineering control in public spaces is limited by the hazardous nature of conventional UV lamps, which are Mercury (Hg)-based and emit a peak wavelength (254 nm) that penetrates human skin and is carcinogenic. Recent advances in the development and production of Krypton Chlorine (KrCl) excimer lamps hold promise in this regard, as these emit a shorter peak wavelength (222 nm) and are recently being produced to filter out emission above 240 nm. However, the disinfection kinetics of KrCl UV excimer lamps against SARS-CoV-2 are unknown. Here we provide the first dose response report for SARS-CoV-2 exposed to a commercial filtered KrCl excimer light source emitting primarily 222 nm UV light (UV₂₂₂), using multiple assays of SARS-CoV-2 viability. Plaque infectivity assays demonstrate the pseudo-first order rate constant of SARS-CoV-2 reduction of infectivity to host cells to be 0.64 cm²/mJ (R² = 0.95), which equates to a D₉₀ (dose for 1 log₁₀ or 90% inactivation) of 1.6 mJ/cm². Through RT-qPCR assays targeting the nucleocapsid (N) gene with a short (<100 bp) and long (∼1000 bp) amplicon in samples immediately after UV₂₂₂ exposure, the reduction of ability to amplify indicated an approximately 10% contribution of N gene damage to disinfection kinetics. Through ELISA assay targeting the N protein in samples immediately after UV₂₂₂ exposure, we found no dose response of the ability to damage the N protein. In both qPCR assays and the ELISA assay of viral outgrowth supernatants collected 3 days after incubation of untreated and UV₂₂₂ treated SARS-CoV-2, molecular damage rate constants were similar, but lower than disinfection rate constants. These data provide quantitative evidence for UV₂₂₂ doses required to disinfect SARS-CoV-2 in aqueous solution that can be used to develop further understanding of disinfection in air, and to inform decisions about implementing UV₂₂₂ for preventing transmission of COVID19.