Sensitivity of airborne transmission of enveloped viruses to seasonal variation in indoor relative humidity

TL;DR

This study uses a detailed aerosol model to analyze how indoor relative humidity influences airborne virus transmission, revealing that dry winter conditions slow virus inactivation and increase infection risk in poorly ventilated spaces.

Contribution

It provides a novel quantitative analysis of how seasonal indoor humidity variations affect airborne virus transmission, specifically for SARS-CoV-2, using the QuaRAD model.

Findings

Dry indoor conditions slow virus inactivation in winter.

In poorly ventilated spaces, lower humidity increases active virion concentration.

Particle settling velocity is not significantly affected by humidity.

Abstract

In temperate climates, infection rates of enveloped viruses peak during the winter. While these seasonal trends are established in influenza and human coronaviruses, the mechanisms driving the variation remain poorly understood and thus difficult to extend to similar viruses like SARS-CoV-2. In this study, we use the Quadrature-based model of Respiratory Aerosol and Droplets (QuaRAD) to explore the sensitivity of airborne transmission to the seasonal variation in indoor relative humidity across the wide range of relevant conditions, using SARS-CoV-2 as an example. Relative humidity impacts the evaporation rate and equilibrium size of airborne particles, which in turn may impact particle removal rates and virion viability. Across a large ensemble of scenarios, we found that the dry indoor conditions typical of the winter season lead to slower inactivation than in the more humid summer season; in poorly ventilated spaces, this reduction in inactivation rates increases the concentration of active virions, but this effect was important when the susceptible person was farther than 2 m downwind of the infectious person. On the other hand, changes in particle settling velocity with relative humidity did not significantly affect the removal or travel distance of virus-laden scenarios.