Impact of poultry vaccination on H5 avian influenza transmission and evolution
A study published in Scientific Advances examines the impact of mass vaccination of poultry against H5 subtypes of avian influenza virus (AIV) on the spread of the virus, with an acknowledgment that such vaccination might also accelerate viral evolution. This research explores the dynamics of AIV lineages among both vaccinated and unvaccinated poultry, as well as wild birds, from 1996 to 2023.
The findings indicate that vaccination in poultry influences transmission dynamics, with unvaccinated poultry exhibiting greater susceptibility to infections from wild birds. This observation suggests that vaccination may serve as a barrier to viral spread.
The analysis reveals a shift from a lineage that circulated among Chinese poultry to one that is now prevalent among wild birds. The lineage from wild birds has been frequently transmitted to unvaccinated European poultry, whereas the spillover from wild birds to vaccinated poultry appears to be hindered.
In the context of the mass poultry vaccination strategy implemented in China since 2005, the spread of H5 AIV has been relatively well controlled. Interspecies transmission of these viruses to or from Chinese poultry seems to be limited. However, the lineage associated with Chinese poultry may have undergone more antigenic evolution compared to other AIV lineages. It is suggested that this particular lineage has experienced greater vaccine-driven selection pressure than its counterparts. The study does not establish a causal relationship, indicating that further virological research is necessary to directly test this hypothesis.
Overall, the findings imply that while vaccination may diminish the transmission of AIV within vaccinated populations, it might concurrently foster an environment where the virus adapts to evade the immune responses of vaccinated hosts, potentially heightening the risk of spillover to unvaccinated populations.
In conclusion, although vaccination in Asian poultry has likely reduced the interspecies transmission of these viruses, the study identifies elevated rates of hemagglutinin (HA) molecular evolution and adaptation in H5 AIV among Chinese poultry following the introduction of vaccination.