In IVEA, we aim to determine how environmental coditions control the physicochemical properties of expiratory aerosols, and how these in turn affect influenza virus infectivity. We hypothesize that virus infectivity is governed by the very fast kinetics of aerosol drying after exhalation, resulting in transient states with thermodynamic non-equilibrium concentrations of organics, salts, surfactants and water in the aerosol matrix, and affecting pH, all of which vary as function of ambient conditions (relative humidity and temperature). Specifically, our objectives are to:

• characterize the composition, morphology and properties of aerosol generated from different respiratory fluids—containing varying portions of mucus—as a function of relative humidity and temperature;
• determine the infectivity of different influenza virus strains in expiratory aerosols under varying conditions;
• identify the physicochemical aerosol properties that govern influenza virus inactivation in expiratory aerosols and determine the involved mechanisms of virus inactivation;
• integrate the results into a comprehensive biophysical aerosol model enabling predictions of the spatiotemporal range of aerosol transmission pathways of different influenza virus strains under various ambient conditions.

Using innovative instrumentation and materials, we tackle these challenges as an interdisciplinary team of aerosol chemists and physicists and environmental and molecular virologists. This unique composition of expertise will allow us to link aerosol physics and chemistry with biological effects. This work aims to produce unprecedented insights into the stability and infectivity of influenza viruses in aerosols under a wide range of ambient conditions. Depending on the outcome of this project, these results may be highly relevant for influenza prevention. The project will inform and support health care policy at the national and international level by facilitating the design of intervention strategies to reduce influenza spread. For example, maintaining indoor-RH at medium levels may be a simple, yet effective strategy to control aerosol transmission of influenza in high-risk settings, such as hospitals or schools. Our findings may furthermore yield basic principles that also apply to the transmission of other respiratory or enteric pathogens, such as norovirus or SARS-CoV-2, contained in aerosols generated from diverse body fluids.