Rapid, dose-dependent and efficient inactivation of surface dried SARS-CoV-2 by 254 nm UV-C irradiation

Background: The COVID-19 pandemic urges for cheap, reliable, and rapid technologies for disinfection and decontamination. One frequently proposed method is ultraviolet (UV)-C irradiation. UV-C doses necessary to achieve inactivation of high-titre SARS-CoV-2 are poorly defined. Aim: We investigated whether short exposure of SARS-CoV-2 to UV-C irradiation sufficiently reduces viral infectivity and doses necessary to achieve an at least 6-log reduction in viral titres. Methods: Using a box and two handheld systems designed to decontaminate objects and surfaces, we evaluated the efficacy of 254 nm UV-C treatment to inactivate surface dried high-titre SARS-CoV-2. Results: Drying for 2 hours did not have a major impact on the infectivity of SARS-CoV-2, indicating that exhaled virus in droplets or aerosols stays infectious on surfaces for at least a certain amount of time. Short exposure of high titre surface dried virus (3–5*10^6 IU/ml) with UV-C light (16 mJ/cm(2)) resulted in a total inactivation of SARS-CoV-2. Dose-dependency experiments revealed that 3.5 mJ/cm(2) were still effective to achieve a > 6-log reduction in viral titres, whereas 1.75 mJ/cm(2) lowered infectivity only by one order of magnitude. Conclusions: SARS-CoV-2 is rapidly inactivated by relatively low doses of UV-C irradiation and the relationship between UV-C dose and log-viral titre reduction of surface residing SARS-CoV-2 is nonlinear. Our findings emphasize that it is necessary to assure sufficient and complete exposure of all relevant areas by integrated UV-C doses of at least 3.5 mJ/cm(2) at 254 nm. Altogether, UV-C treatment is an effective non-chemical option to decontaminate surfaces from high-titre infectious SARS-CoV-2.