Solar UV-B/A radiation is highly effective in inactivating SARS-CoV-2

Abstract

Solar UV-C photons do not reach Earth’s surface, but are known to be endowed with germicidal properties that are also effective on viruses. The effect of softer UV-B and UV-A photons, which copiously reach the Earth’s surface, on viruses are instead little studied, particularly on single-stranded RNA viruses. Here we combine our measurements of the action spectrum of Covid-19 in response to UV light, Solar irradiation measurements on Earth during the SARS-CoV-2 pandemics, worldwide recorded Covid-19 mortality data and our “Solar-Pump” diffusive model of epidemics to show that (a) UV-B/A photons have a powerful virucidal effect on the single-stranded RNA virus Covid-19 and that (b) the Solar radiation that reaches temperate regions of the Earth at noon during summers, is sufficient to inactivate 63% of virions in open-space concentrations (1.5 × 103 TCID50/mL, higher than typical aerosol) in less than 2 min. We conclude that the characteristic seasonality imprint displayed world-wide by the SARS-Cov-2 mortality time-series throughout the diffusion of the outbreak (with temperate regions showing clear seasonal trends and equatorial regions suffering, on average, a systematically lower mortality), might have been efficiently set by the different intensity of UV-B/A Solar radiation hitting different Earth’s locations at different times of the year. Our results suggest that Solar UV-B/A play an important role in planning strategies of confinement of the epidemics, which should be worked out and set up during spring/summer months and fully implemented during low-solar-irradiation periods.

UV and violet light can Neutralize SARS-CoV-2 Infectivity

“…It should be noted that whereas for both bacteria and DNA viruses the inactivation observed in the UV-A is 10 −5 -10 −6 times lower than that observed in the UV-C region, for RNA viruses the inactivation power is only marginally lower in the UV-A than in the UV-C region (just about 100-1000 times lower at 366 nm). Taking into account that the Solar illumination in the UV-A region is much larger than in the UV-B (95% of UV-A and 5% of UV-B), these results might justify the acknowledged seasonal behavior of the outbreaks of airborne viruses, including corona [ 35 , 52 , 53 ] and influenza viruses [ 54 , 55 ]. In this respect, we would like to stress how it is crucial to have the specific data of the target microorganism to develop reliable solar inactivation and/or seasonal models and how Lytle and Sagripanti action spectrum cannot be considered as a reference trend.…”

“…UV-A and UV-B radiations, on the other hand, reach the earth surface with different intensities, which depend on the season, the latitude, and the weather conditions. The effect of solar UV-A and UV-B radiation on microorganisms [ 31 , 32 ] and on the seasonal behavior of infectious diseases has been extensively discussed [ 33 , 34 ], and recent predictive models suggest that SARS-CoV-2 infection is indeed solar-sensitive [ 35 , 36 ]. Solid, convincing and reproducible experimental data on the possible virucidal effects of UV-A and UV-B and their correlation with SARS-CoV-2 epidemiology are nevertheless missing.…”

Role of meteorological factors on SARS-CoV-2 infection incidence in Italy and Spain before the vaccination campaign. A multi-city time series study

“…For relative humidity, high values favour the increase and the fall of the droplet size reducing the risk of infection ( Ahlawat et al, 2020 ). The results of UV radiation were unexpected under the hypothesis that UV light could cause the inactivation of viruses in the air and on surfaces ( Nicastro et al, 2021 , p. 2). The non-linear association in our study, with low and high levels of radiation associated with lower risk, could be explained by the effects of weather-dependent human behaviour change and warrants further investigation.…”

Evidence for the dependence of the SARS-Cov-2 Delta high diffusivity on the associated N:G215C nucleocapsid mutation

“…Actually, several works pointed out the strong seasonality of COVID-19, with Summer months experiencing much less infection diffusion and milder disease (e.g. De Natale et al, 2020b;Nicastro et al, 2021).…”