HK CHP Reports 2 Mainland H9N2 Cases & WHO Clarifies Report On Indian H5N1 Case

   

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It's no secret that China tends to be cryptic in their public descriptions of avian flu cases, often only providing an onset date, the patients age and gender, and the province where it occurred.  

Additional details on the patient's outcome, or exposures, are often only later revealed in the WHO's WHO: Influenza at the Human-Animal Interface Summary and Assessment, and those are often scant. 

Today's report from Hong Kong's CHP on two recent (albeit from May & June) H9N2 cases on the Mainland (see above) provides even less information than usual as ages and genders are not included. 

Typically, H9N2 presents as a mild infection, and is most often reported in children. For reasons that aren't clear, female cases have outnumber males by a considerable margin (cite).

But over the past 6 months 31% (5 of 16) cases reported by China (with ages provided) have been in adults. At least 4 were reported as hospitalized, 2 with severe illness.  

So the sudden and unexplained replacement of age and gender data with `an individual' in this CHP report is disappointing, as these metrics are among the few we have to track whether H9N2's behavior is changing. 

It is not an idle concern, as the H9N2 virus continues to evolve, and diversify. The CDC has designated 2 different lineages (A(H9N2) G1 and A(H9N2) Y280) as having some pandemic potential (see CDC IRAT SCORE), and several candidate vaccines have been developed.

H9N2 also easily reassorts with, and often enhances, other novel influenza viruses (including H7N9, H5N1, and H5N6), making it an important viral co-conspirator (see Vet. Sci.: The Multifaceted Zoonotic Risk of H9N2 Avian Influenza).

Despite decades of mandated use of vaccines, H9N2 remains poorly controlled in Chinese poultry (see J. Virus Erad.: Ineffective Control Of LPAI H9N2 By Inactivated Poultry Vaccines - China), which has led to the creation and spread of numerous  genotypes.

While I hope these reporting changes are temporary, as we've discussed often over the past couple of years (see here, here, here, and here), the sharing of emerging disease information has deteriorated badly around the world since 2020. 

We've also a clarification on a report last week from the WHO on a fatal H5N1 case in India from last May.  The original report read:

A(H5N1), India

A human infection with an H5 clade 2.3.2.1a A(H5N1) virus was detected in a sample collected from a man in Khulna state in May 2025, who subsequently died. Genetic sequence data are available in GISAID (EPI_ISL_19893416; submission date 4 June 2025; ICMR-National Institute of Virology; Influenza).

As I pointed out last week, Khulna is not a state in India, but it is a region in Bangladesh (where two recent H5 cases were previously reported).  

Today the WHO's SERO Epi bulletin (14th edition 2025) has a brief update (see below) indicating this case originated from Karnataka State, in the southwestern part of India. 

 

While H9N2 remains far from our biggest pandemic threat, a recent review of it's potential can be found at Nature: Genetic diversity of H9N2 avian influenza viruses in poultry across China and implications for zoonotic transmission.

Which is why continued reports of cases in China (and elsewhere in the world) are worthy of our attention.