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

TL;DR

This study demonstrates that solar UV-B/A radiation effectively inactivates SARS-CoV-2, potentially explaining seasonal patterns of COVID-19 and informing epidemic control strategies based on solar radiation levels.

Contribution

It provides the first comprehensive analysis of UV-B/A's virucidal effect on SARS-CoV-2 using combined measurements, modeling, and epidemiological data.

Findings

UV-B/A radiation can inactivate 63% of SARS-CoV-2 virions in less than 2 minutes.

Seasonal variations in UV-B/A exposure correlate with COVID-19 mortality trends.

Solar UV-B/A plays a significant role in the natural inactivation of the virus outdoors.

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$-$19 in response to UV light, Solar irradiation measurements on Earth during the SARS$-$CoV$-$2 pandemics, worldwide recorded Covid$-$19 mortality data and our 'Solar$-$Pump' diffusive model of epidemics to show that (a) UV$-$B$/$A photons have a powerful virucidal effect on the single$-$stranded RNA virus Covid$-$19 and that (b) the Solar radiation that reaches temperate regions of the Earth at noon during summers, is sufficient to inactivate 63\perc of virions in open$-$space concentrations (1.5 x 103 TCID50$/$mL, higher than typical aerosol) in less than 2 min. We conclude that the characteristic seasonality imprint displayed world$-$wide by the SARS$-$Cov$-$2 mortality time$-$series throughout the diffusion of the outbreak (with temperate regions showing clear seasonal trends and equatorial regions suffering, on average, a systematically lower mortality), might have been efficiently set by the different intensity of UV$-$B$/$A Solar radiation hitting different Earth's locations at different times of the year. Our results suggest that Solar UV$-$B$/$A play an important role in planning strategies of confinement of the epidemics, which should be worked out and set up during spring$/$summer months and fully implemented during low$-$solar$-$irradiation periods.