A new international study suggests that vaccines may be driving bird flu evolution, as efforts to contain the spread of the virus face increasing challenges.
Amid growing concerns about potential human cases, a new analysis has found increasingly resilient bird flu strains are arising globally. Despite this, significant concerns for rapidly spreading H5 bird flu infections remain isolated within avian populations.
Mass Poultry Vaccines
In many countries, farmers feed livestock with steady doses of antibiotics and vaccines to keep them healthy until their turn at the slaughterhouse or as they continue to produce milk and eggs for animal agriculture.
The highly pathogenic H5 group of avian influenza virus, which includes H5N1, came into focus in the new research. The team studied H5 viruses in the wild and among poultry farming in agriculture, with an eye on comparing countries where poultry vaccinations are or are not routine practice. Currently, H5N6 is the most common variation in China, and its evolution may be vaccine-driven.
“As avian influenza continues to pose considerable challenges to wild and domestic animals, our research can help inform the development of preventive measures against AIV, such as global vaccination policies,” Bingying Li and colleagues write.
Evolving H5 Bird Flu Viruses
H5 viruses have been spreading worldwide for decades and are continually evolving. Many countries have implemented large-scale vaccinations to mitigate economic and food stability concerns.
However, large-scale vaccination may only accelerate evolution, producing more robust viruses that can easily circumvent vaccines’ protection. The new study maps these transmissions across wild, agricultural, and vaccinated and unvaccinated bird populations.
Researching Bird Flu Transmission
The researchers conducted a phylogenetic analysis of hemagglutinin (HA) sequences from worldwide viral samples from 1996 to 2023. The team utilized public databases like the international cooperative GISAID and the US National Institute of Health’s GenBank. HA specifically aids in viral binding and infection. The results showed that vaccination did minimize transmission from wild birds to poultry. However, countries like China with high vaccination rates also incurred much more rapid virus evolution than largely unvaccinated countries like Bangladesh and Indonesia.
While the data may be troubling, precautions are being taken. Biosecurity teams keep UK poultry separated from wild populations to minimize infection opportunities. Some countries rely more heavily on vaccination, as agricultural conditions make separating poultry from wild birds more challenging.
When The Debrief asked co-author Oliver Pybus of the Royal Veterinary College University of Oxford whether slowing the spread or virus evolution was the most pressing concern, he said, “That’s a really interesting question. In short, they are intimately linked. Virus evolution only occurs when the virus transmits, so the more opportunities for infection there are, the greater the potential for more virus adaptation.”
Where Bird Flu Goes Next
While H5N1 bird flu has led to 67 confirmed cases and even one death in the United States, according to the CDC, the forbidding virus has yet to become a significant problem for humans. Pybus said that his work did not raise any immediate concern about the imminent spread of the virus to humans.
“All previous human flu pandemics were caused by H1 or H3 viruses. We still don’t fully understand why H5 has not evolved to transmit among humans,” Pybus commented. But he did note that to keep poultry populations safe, “It’s clear that we need to enhance our surveillance of people who come into frequent contact with wild birds, poultry, and infected cattle.”
Despite alarms that have been raised about potential human spread, the team believes that keeping an eye on bird populations is the crucial next step. “Experimental work is needed to determine what has caused the change in virus evolution, and to test the hypothesis that avian flu might evolutionarily adapt in response to poultry vaccination,” Pybus explained.
The paper “Association of Poultry Vaccination with Interspecies Transmission and Molecular Evolution of H5 Subtype Avian Influenza Virus” appeared on January 22, 2025, in Science Advances.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.