Avian Flu Diary: WHO Influenza at the human-animal interface (Aug 7th)

#19,299

The WHO has released an update (dated Aug 7th, but posted overnight) of human novel flu infections reported between July 8th and Aug 7th. Included are 8 H9N2 cases from Mainland China, and 1 H5N1 case from Cambodia (all previously reported).

This report also confirms the H5 case reported from Bangladesh in July has been confirmed as H5N1.

For reasons well above my pay grade, reporting from Hong Kong's CHP on H9N2 cases has been a bit chaotic this month (reporting the same 4 recent cases as `new' for the past 3 weeks running), and the WHO's weekly WPRO avian flu report hasn't been updated since Aug 7th.

What we can say, however, is that China (along with a recent case in Hong Kong) has seen an uptick in reported H9N2 cases this summer. Whether this is due to more frequent spillovers, or better surveillance, isn't known.

Despite being clearly zoonotic - LPAI H9N2 is considered a `non-reportable' disease in poultry or wild birds by WOAH (see Terrestrial Animal Code). Complicating matters, China's attempts to control LPAI H9N2 through vaccines have been less than successful.

In 2025's NPJ Vaccines: Impact of Inactivated Vaccine on Transmission and Evolution of H9N2 Avian Influenza Virus in Chickens, we saw evidence that inactivated vaccines failed to prevent - or even reduce - H9N2 in China's poultry, and may have driven viral evolution (including mammalian adaptations).

Several recent Chinese studies have found signs that LPAI H9N2 is becoming better adapted to mammals, warning of its pandemic potential; including:

Two weeks ago, in EM&I: Genetic evolution, phylodynamics, geographic spread of H9N2 avian influenza viruses in China from 2014 to 2025: an increasing potential zoonotic risk, we saw yet another Chinese study warning that H9N2 was accruing mammalian adaptations which increases its zoonotic risk.
Two months ago, in Viruses: Epidemiological and Virological Characteristics of H9N2 Avian Influenza Virus in Jiangsu Province, China, 2024, researchers warned that that Jiangsu’s circulating H9N2 viruses have acquired human receptor preference and mammalian adaptation, posing silent infection and pandemic risks

Last October, in China CDC Weekly: Epidemiological and Genetic Characterization of Three H9N2 Viruses Causing Human Infections, investigators reported a number of indicators of increased mammalian adaptation within the virus, including an enhanced ability to infect upper respiratory (α2,6-sialic acid) tract receptors, and a number of HA protein mutations, including; H191N, A198V, Q226L, and Q234L.

The Asian Y280/G57 lineages have shown increasing signs of mammalian adaptation (see EM&I: Enhanced Replication of a Contemporary Avian Influenza A H9N2 Virus in Human Respiratory Organoids)), while the African and Middle Eastern Lineages (mostly European G1-like) are older and less evolved.

Last summer, in Nature: Genetic diversity of H9N2 avian influenza viruses in poultry across China and implications for zoonotic transmission, researchers reported rising prevalence of key mutations associated with increased infectivity and pathogenicity in mammals.

While H9N2 doesn't garner the kind of headlines that H5N1 gets, our own CDC lists two lineages (A(H9N2) G1 and A(H9N2) Y280) as having at least some pandemic potential, and several candidate vaccines have been developed.