Inactivation mechanisms of influenza A virus within the micro-environment of expiratory bioaerosols

Approximately 400’000 deaths are associated with influenza virus every year. Whilst currently dwarfed by the COVID-19 pandemic, influenza continues to circulate within the human population since the first recorded 1918 pandemic over a century ago. During this pandemic, influenza virus killed an estimated 50 million people, and recurrent clusters of human infection with avian influenza viruses now pose a real risk for a repeat pandemic scenario. Health-care policies aim to reduce the public health and economic impacts of influenza and similar respiratory diseases by preventing virus transmission. However, we possess an incomplete understanding of transmission pathways, particularly the aerosol route. To provide new insight, we have biophysically modelled the microenvironment of the expiratory aerosol. Surprisingly, the model shows rapid acidification of the bioaerosol down to pH ~4 after exposure to indoor air. The effect of such an acidic aerosol micro-environment on respiratory viruses has never been subject to a targeted investigation.