Sunlight Inactivation of Influenza A Virus and Bacteriophages on Surfaces

Seasonal epidemics and pandemics of influenza cause a large public health burden, with transmission occurring via direct contact and contaminated fomites. Sunlight has been shown to inactivate viruses in water but its effect on viruses on surfaces remains poorly understood. This study investigated the sunlight inactivation of bacteriophage MS2, bacteriophage Phi6, and influenza A virus H1N1 (IAV) on plastic surfaces. Our findings demonstrate that sunlight can rapidly inactivate viruses on a plastic surface, with the time required for 99% of inactivation ranging from 2.05-4.22 h for MS2, 0.72-0.83 h for Phi6, and 0.26-0.35 h for IAV. Human saliva protected MS2 against sunlight inactivation, but had no effect on Phi6 and IAV. IAV exhibited similar inactivation rate constants under natural and simulated sunlight. IAV whole genome photodamage, estimated from RT-ddPCR measurements of 8 individual genes using a single-hit extrapolation model, overestimates loss of IAV infectivity, suggesting that genome damage may cause inactivation, yet also calling into question whether assumptions of the extrapolation model are appropriate for sunlight. Our work indicates that natural sunlight can substantially reduce the survival of influenza virus on outdoor surfaces, thereby lowering the fomite-mediated transmission of respiratory disease in sunlit environments.