The H9N2 avian influenza virus, long considered a threat mainly to poultry, is now showing an increasing ability to infect humans, according to Innovanews, citing a new study published in Nature Microbiology. Chinese scientists, led by Professors Bi Yuhai, Gao Fu, and Shi Weifen, conducted a large-scale analysis of H9N2’s genetic diversity and evolution, uncovering alarming signs of the virus adapting to the human body.

H9N2 was first identified in China in 1994 and has remained the dominant avian influenza subtype among domestic poultry, despite widespread vaccination efforts. However, in recent years, cases of human infection have increased, raising serious concerns in the scientific community, Planet Today reports.

Researchers from the Chinese Academy of Sciences’ Institute of Microbiology (CASCIRE) and other institutions monitored the virus from 2014 to 2023 by analyzing samples collected from live poultry markets. They found that the virus is actively mutating, with at least ten different genetic subtypes of H9N2 currently circulating, reducing the effectiveness of existing vaccines.

A key feature of the latest strains is the emergence of mutations that facilitate the virus’s entry and replication in human cells. Notably, the HA-L226 mutation, which enhances the virus’s ability to bind to receptors on human cells, was found in 99.46% of the samples. Additionally, 96.17% of strains carried the NP-N52 mutation, which helps the virus evade MxA, a protective protein involved in the human immune response. The PB2-V627 mutation—detected in 32.61% of the viruses—promotes faster replication in mammalian cells. These changes significantly increase the risk of transmission between animals and humans, as confirmed by experiments on ferrets and guinea pigs, which serve as models for studying zoonotic infections.

Professor Bi Yuhai noted, “These mutations allow H9N2 to not only effectively infect birds but also adapt to the human body, making it crucial to strengthen epidemiological surveillance and develop new vaccines.” Despite long-term vaccination efforts against H9N2 in China, the virus remains highly prevalent and continues to evolve, potentially leading to new strains with even greater human infectivity.

The study also emphasized the need for more effective vaccines that induce not only humoral but also cellular immunity and enhance mucosal protection in the respiratory tract. Scientists warn that without timely vaccine updates and strengthened virus monitoring, H9N2 could spark a new pandemic.

While the research focused on China, where the virus is most widespread, experts noted that H9N2 is also present in other parts of Asia, the Middle East, and Africa. Further studies in these regions are needed to better assess the threat. Researchers continue to investigate the virus’s adaptation mechanisms and are working on strategies to prevent its further spread among humans.

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