Advancing A(H5N1) influenza risk assessment in ferrets through comparative evaluation of airborne virus shedding patterns

Recent A(H5N1) zoonotic cases linked to poultry and cattle in North America highlight the urgent need to assess the pandemic potential of emerging strains. Using male ferrets, we evaluate two B3.13 and two D1.1 genotype A(H5N1) viruses isolated from humans and observe fatal disease and varying capacities for direct contact transmission. To enhance pandemic risk assessment, we conduct aerosol sampling using cyclone BC251 and water condensation capture-based SPOT samplers and perform comparative analyses to include additional A(H5N1), A(H9N2), A(H7N9), and A(H1N1)pdm09 strains with known transmissibility profiles. Although none of the A(H5N1) strains transmit via the air, B3.13 viruses are detected at significantly higher levels compared to D1.1 strains. Here we show strong correlations between viral loads in nasal washes, airborne virus shedding, and transmissibility in ferrets, highlighting the value of these metrics for identifying zoonotic influenza viruses that may be adapting toward increased transmission potential.