Persistence of Phi6, a SARS-CoV-2 surrogate, in simulated indoor environments: Effects of humidity and material properties.

The SARS-CoV-2 virus caused the COVID-19 pandemic and brought major challenges to public health. It is transmitted via aerosols, droplets, and fomites. Among these, viral transmission through fomites is not well understood although it remains a very important transmission route. This motivated us to study how fomites play a role in viral transmission within controlled indoor environments. To achieve this, we investigated viral aerosol persistence on fomites under different humidity levels to mimic the built environment. We developed a protocol to study the effect of humidity on viral infectivity using a full-scale environmental chamber. The results show that the infectivity of aerosolized Phi6 in air decreased by ≥ 1 log10 as the relative humidity (RH) increased from 25% to 75% but then increased by ≥ 1 log10 as the RH further increased to 85%, resulting in a characteristic V-shape curve which varied with exposure time. Consistently, we show that although material properties may impact viral persistence, changes in the local humidity more significantly influence viral persistence on fomites. These results provide new insights into indoor fomite-mediated viral transmission under different environmental conditions. These findings will help guide the design of more effective strategies for viral control in indoor environments.