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As an LPAI (low path avian influenza), H9N2 is not considered a `reportable' disease by WOAH (formerly the OIE), even though it is clearly zoonotic.
In addition to > 140 confirmed human infections (see FluTrackers list), seroprevalence studies have shown people with exposure to infected poultry often develop H9 antibodies, suggesting mild or asymptomatic infection.
H9N2 is poorly controlled in Chinese poultry, despite the use of vaccines (see J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China), which has led to the creation and spread of numerous of genotypes.H9N2 also reassorts with, and often enhances, other novel influenza viruses (including H7N9, H5N1, and H5N6), making it an important co-conspirator (see Vet. Sci.: The Multifaceted Zoonotic Risk of H9N2 Avian Influenza).
In the second half of 2024 we saw a noticeable uptick in H9N2 reports coming out of China (see Hong Kong CHP: 7 Recent H9N2 Cases Reported From the Mainland) , along with cases reported from India, Vietnam, and Ghana.While LPAI H9N2 is admittedly not at the very top of our list of pandemic concerns, the CDC has 2 different lineages (A(H9N2) G1 and A(H9N2) Y280) on their short list of influenza viruses with zoonotic potential and several candidate vaccines have been developed.
Details are scant, but today Hong Kong's CHP has announced 2 new H9N2 infections on the mainland; the first occurring in late December (M,2) and a second with onset on January 8th (M,15).
While most H9N2 infections have been mild - a few hospitalizations and at least two deaths have been reported. Nearly 90% of all known cases have been reported by China.VOLUME 21, NUMBER 6 Reporting period: Feb 2, 2025 – Feb 8, 2025 (Week 6) (Published on February 11, 2025)
