H7 highly pathogenic avian influenza viruses (HPAIVs) pose a potential threat to avian and human health due to their ability to infect numerous species and cause severe disease. H7 HPAIV outbreaks severely impact the poultry industry and result in significant socioeconomic losses, as exemplified by the 2024 H7 HPAIV outbreaks in Australia.
H7 HPAIVs continue to evolve antigenically, enabling evasion of the host immune response. The mechanism contributing to the antigenic evolution of AIVs are antigenic drift and shift. Antigenic drift describes the accumulation of mutations in antigenic regions that result in immune evasion. The influenza surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), are the primary targets of the host immunological response to influenza infection. The antigenic drift of H7 HPAIVs are closely monitored to ensure that vaccine seed strains are protective against circulating strains. It is therefore crucial to monitor H7 HPAIV antigenic drift to inform pandemic preparedness frameworks.
Here, the antigenic drift of A/chicken/NSW/2012 H7N7 HPAIV under immunological pressure was characterised. Specifically, we assessed the antigenic drift of the surface glycoproteins, HA and NA. H7N7 HPAIV was incubated with increasing concentrations of chicken polyclonal homologous antisera or naïve chicken serum before passaging in embryonated chicken eggs. Viral genetic diversity was monitored by next generation sequencing to determine changes in regions encoding antigenic epitopes. Hemagglutinin inhibition and neuraminidase inhibition assays will be used to characterise the impact of antigenic escape mutations on antigenicity. This data informs vaccine strain selection and helps us forecast the antigenic drift of H7 HPAIV.