Estimated Inactivation of Coronaviruses by Solar Radiation With Special Reference to COVID‐19

Abstract

Using a model developed for estimating solar inactivation of viruses of biodefense concerns, we calculated the expected inactivation of SARS-CoV-2 virus, cause of COVID-19 pandemic, by artificial UVC and by solar ultraviolet radiation in several cities of the world during different times of the year. The UV sensitivity estimated here for SARS-CoV-2 is compared with those reported for other ssRNA viruses, including influenza A virus. The results indicate that SARS-CoV-2 aerosolized from infected patients and deposited on surfaces could remain infectious outdoors for considerable time during the winter in many temperate-zone cities, with continued risk for re-aerosolization and human infection. Conversely, the presented data indicate that SARS-CoV-2 should be inactivated relatively fast (faster than influenza A) during summer in many populous cities of the world, indicating that sunlight should have a role in the occurrence, spread rate and duration of coronavirus pandemics.

Why does the COVID-19 outbreak in Mexico seem to be slower? Some hypotheses for testing

“…The effect of natural and arti cial UV on virus inactivation has been extensively studied. For example, the in uenza virus is inactivated by up to 99% if exposed to full sunlight during a single day in Mexico City, but this value lowers to 66% in the winter (Sagripanti and Lyte 2007;Sagripanti and Lytle 2020). Another study demonstrated that aerosolized MHV Coronavirus could be highly sensitive to 254 nm UV-C, but it is dependent on the culture medium (Walker and Ko 2007).…”

UVA radiation could be a significant contributor to sunlight inactivation of SARS-CoV-2

“…to 37% of the initial value), and is written as D 37,UVC [6]. Based on genome size, for Coronaviridae , they estimated D 37,UVC between 2.5-3.9 J/m 2 , and D = 3.0 J/m 2 for SARS-CoV-2 [7]; this value is used in the calculations presented here. Although no UVC reaches the Earth’s surface, longer wavelengths can still affect viral RNA, albeit with decreased sensitivity.…”

“…Sagripanti & Lytle [7] later calculated inactivation rates for SARS-CoV-2, for several worldwide locations at different times of the year. As will be shown later in Figure 1, the experimentally observed inactivation rates in [2,3] are significantly faster than predicted by the model in [6,7]. In addition, the observed dependence on the medium composition is not consistent with this medium-independent model.…”

“…(A, D): high simulated sunlight, (B, E): medium simulated sunlight, (C, F): low simulated sunlight. Purple dotted line: UVB-only theory (Equation 3) with D 37,UVC = 3.0 J/m 2 [6,7]. Green dot-dashed line: UVB-only theory with D 37,UVC from a fit to all data.…”

“…It is generally expected that UVB acts on viruses through a direct, endogenous pathway [5], as has been modeled by [6,7]. Inactivation by UVA has been established for viruses in presence of sensitizers, through an exogenous, indirect pathway, for example by damaging the virus’s envelope and thereby disrupting attachment and entry [5,9].…”