#19,271
Three days ago we looked at an HK report on 3 recent human infections with avian H9N2 on the Chinese Mainland (Guangxi Province, Jiangsu Province, Guangdong Province), all reported in late June.
Today, the WHO's WPRO (Western Pacific Regional Office) reports 4 more human infections, all occurring in the first half of July, making 7 H9N2 cases reported by China over a period of roughly 3 weeks.
We've often discussed the difficulty in detecting cases, since most H9N2 infections are mild or moderate, and clinically indistinguishable from seasonal flu, meaning we've no idea how many cases we may be missing.
As the following chart illustrates, case counts have been rising steadily in recent years, although it isn't known whether this trend is due to increased spillover of H9N2 to humans, or better surveillance.
The 7 cases from the last 2 reports are spread across 6 provinces, and most are said to have either direct or potentially indirect exposure to poultry. Of these seven cases, three adult patients reportedly had (unspecified) comorbidities and were hospitalized, while the four pediatric cases had mild illness.
Human infection with avian influenza A(H9N2) virus
From 24 to 30 July 2026, four new cases of human infection with avian influenza A(H9N2) virus were reported to WHO in the Western Pacific Region. All four cases were from China. The cases included;
- a 72-year-old female from Jiangxi Province with symptom onset on 5 July 2026;
- a 12-year-old male from Jiangsu Province with symptom onset on 6 July 2026;
- a 3-year-old female from Gansu Province with symptomonset on 11 July 2026;
- and a 58-year-old female from Yunnan Province with symptom onset on 13 July 2026.
The four cases reported were geographically distinct from each other. One case reported direct exposure to live-poultry, while three had potential exposure related to live-poultry stalls or wet market visits. Two cases with underlying chronic respiratory disease conditions were hospitalized and subsequently discharged. The remaining two cases experienced mild illness, were not hospitalized and had recovered at the time of reporting.
Since 2015, a total of 177 cases of human infection with avian influenza A(H9N2), including two deaths (both with underlying conditions), have been reported to WHO in the Western Pacific Region. Of these, 174 were reported from China, two were from Cambodia, and one was from Viet Nam.
Most human infections with avian influenza A(H9N2) have been associated with exposure to infected poultry or contaminated poultry environments, and the majority of cases have been mild. Sporadic human infections continue to be expected in areas where H9N2 viruses circulate in poultry populations. Current evidence indicates that H9N2 viruses have not acquired the ability for sustained human-to-human transmission, and the risk of further community-level spread remains low.
Despite being clearly zoonotic - LPAI H9N2 is considered a `non-reportable' disease in poultry or wild birds by WOAH (see Terrestrial Animal Code). As a result, there are huge gaps in surveillance and reporting around the world.
At the same time we've seen a growing number of studies - mostly out of Asia - warning of its growing adaptation to mammalian hosts (see EM&I: Enhanced Replication of a Contemporary Avian Influenza A H9N2 Virus in Human Respiratory Organoids).
Last October the Chinese CDC Weekly published a detailed report (see Epidemiological and Genetic Characterization of Three H9N2 Viruses Causing Human Infections — Changsha City, Hunan Province, China, April 2025) which found:
Three children infected with H9N2 AIV were identified in Changsha in April 2025, and no epidemiological links were found between these mild and sporadic cases. Genetic analysis showed that the H9N2 viruses had enhanced binding ability to upper respiratory tract receptors, particularly the α2,6-sialic acid receptors.
The report goes on describe some of the notable HA mutations suggesting enhanced mammalian adaptation:
Analysis of receptor-binding sites showed that the HA proteins had mutations at amino acid positions H191N, A198V, Q226L, and Q234L, which potentially enhanced the binding ability of the virus to the receptor (5-6).
While there is still no evidence of sustained or efficient human-to-human transmission of H9N2, the virus remains poorly controlled in poultry, and appears on a path towards greater mammalian adaptation.
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.
Whether H9N2 has true pandemic potential is unknown, but between acquiring new mammalian adaptations, and the ease with which it appears to be spilling over into humans, this is definitely a virus worth keeping our eye on.
