Temporal dynamics in divergence and adaptive fixation of the H5 AIV HA gene, in different host-specific lineages. Credit: Science Advances (2025). DOI: 10.1126/sciadv.ado9140
A team of virologists, infectious disease specialists and pathobiologists affiliated with several institutions in China and the U.K. has found possible evidence that bird flu vaccinations are driving virus evolution. In their study published in the journal Science Advances, the group carried out a genetic analysis of hemagglutinin sequences from avian samples collected between 1996 to 2023.
Prior research has shown that the development of a vaccine against a virus is not always the end of the story—oftentimes, the virus will evolve to overcome the vaccine. In this new study, the researchers wondered if that might be the case with H5 subtypes of the avian influenza virus—most specifically, H5N1 and H5N6. Both types are currently infecting birds around the world.
They noted that some countries, such as China, actively pursue poultry vaccinations to slow or stop outbreaks, while others have lower poultry vaccination rates. Such different approaches, the researchers note, offer the opportunity to test whether vaccination efforts are driving the virus to evolve in new ways.
To find out, the team conducted a genetic study of hemagglutinin collected from birds around the world over the years 1996 to 2023. Hemagglutinin is a receptor-binding and membrane fusion glycoprotein—it is produced by viruses to allow them to bind to receptors in a host.
The researchers found, unsurprisingly, that infections occurred more often in birds that were not vaccinated, showing that they do work. They also found that in countries where vaccination is widespread, there was a higher rate of viral evolution compared to evolution rates in countries with lower vaccination rates.
The researchers note that viral evolution of hemagglutinin can lead to resistance against vaccines and can sometimes lead to the virus jumping to other species more easily. They also caution that their findings are not causal; they are instead merely correlative. More research is required to determine whether the vaccines actually cause the evolutionary changes to take place.
More information:
Bingying Li et al, Association of poultry vaccination with interspecies transmission and molecular evolution of H5 subtype avian influenza virus, Science Advances (2025). DOI: 10.1126/sciadv.ado9140
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Possible evidence of bird flu vaccinations driving virus evolution (2025, January 23)
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