Existing data suggest that UVA radiation could be the principal contributor to sunlight inactivation of SARS-COV-2

Abstract:

Recent experiments have demonstrated that SARS-CoV-2 is inactivated by simulated sunlight (Ratnesar-Shumate et al. 2020, J. Infect. 222:214–222). These results have been parameterized by UVB intensity, since UVB is expected to act directly on RNA; this mechanism has also guided modeling efforts (Sagripanti & Lytle 2020, Photochem. Photobiol. In press). Unfortunately, in sunlight, the integrated energy over the UVB range is only a few percent that of UVA, and is significant over a narrower daytime window, thereby limiting its availability for inactivation purposes. Intriguingly, UVA inactivation has previously been demonstrated for other enveloped RNA viruses, through indirect mechanisms involving natural or engineered sensitizers (Nelson et al. 2018, Environ. Sci. Process Impacts, 20:1089–1122). A demonstration that UVA also affects SARS-CoV-2 would imply a much greater inactivation potential than currently expected, and may enable using inexpensive and efficient UVA light sources for disinfection. In this study, we use a model of photo-conversion kinetics, inclusive of both UVA and UVB, to re-examine published data for the inactivation of SARS-CoV-2. We find that a mechanism relying primarily on UVA actually provides a better quantitative explanation for the observed dependence of inactivation rates with sunlight intensity. The UVA sensitivity that we deduce for SARS-CoV-2 is also in good quantitative agreement with previous experiments for inactivation of SARS-CoV-1 due to UVA-only exposure. Our analysis indicates the need for targeted experiments that can separately assess the effects of UVA and UVB on SARS-CoV-2, and that sunlight inactivation models may need to be expanded to also include the effect of UVA.