Melbourne, Australia – Scientists are warning that a lesser-known strain of bird flu, known as H9N2, may have the potential to spark a future pandemic after showing signs of adapting to human cells.
According to research presented this week at the Pandemic Research Alliance International Symposium in Melbourne, the H9N2 virus—historically considered a mild strain—has undergone genetic changes since around 2015 that make it more infectious to people.
Dr. Kelvin To, a clinical microbiologist at the University of Hong Kong, said his team found that a modern version of H9N2 collected in 2024 infected far more human cells than a 1999 sample. The study, published earlier this month in Emerging Microbes & Infections, also showed the updated strain had improved binding to receptors on human cells, a sign it is adapting toward human-to-human spread.
While H9N2 infections in people have been rare—just 173 reported globally since 1998, mostly in China—scientists believe the virus could be circulating unnoticed. Dr. Michelle Wille, of the Peter Doherty Institute for Infection and Immunity, said many cases may be missed because H9N2 typically causes only mild symptoms or is overshadowed by testing for more severe strains such as H5N1.
Currently, there is no evidence of person-to-person transmission, but researchers caution that the virus’s trajectory mirrors early stages seen in other pandemic strains. Experts are calling for stronger international surveillance to track its evolution and detect mutations that could heighten its risk to humans.
