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Although official reports of additional human H5N6 infections in China have (at least, temporarily) shut down over the past month, 2021 has seen a surge in cases, with 26 of the 52 known infections since 2014 occurring over the past 12 months.
Many of these cases were reported over the summer months, a time when transmission of avian viruses is generally at its nadir, and this fall we've seen at least two Chinese CCDC Weekly reports warning that HPAI H5N6 continues to mutate and reassort, and that its threat to public health is increasing.China CCDC Weekly: Genetic Characterization of Two Human A (H5N6) Viruses — Guangxi , China, 2021
CCDC Weekly: Outbreak Report - Five Independent Cases of Human Infection With HPAI H5N6 — Sichuan Province
In recent weeks we've seen several H5N6 risk assessments or statements of concern published by public Health Agencies, including WHO: Assessment of Risk Associated with Influenza A(H5N6) Virus and UK HSA Risk Assessment On HPAI H5N6.
In Early November the CDC published CDC Monitoring HPAI H5N6 In China, where they announced their intention to undertake a new risk assessment of H5N6, which has just been published on their IRAT (Influenza Risk Assessment Tool) list.
The CDC is quick to point out the Influenza Risk Assessment Tool (IRAT) is not meant to be predictive. As stated in their FAQ:
Can the IRAT predict a future pandemic?
No. The IRAT is an evaluative tool, not a predictive tool. Flu is unpredictable, as are future pandemics.
The CDC's IRAT can help planners decide which viruses pose the greatest risks, so they can prioritize their efforts and investments. In 2016, the CDC had only 11 novel flu viruses on their IRAT watch list, but over the the past 5 years we've seen that number double to a record high (n=22).
Since 2014, 52 human infections with highly pathogenic avian influenza (HPAI) A(H5N6) clade 2.3.4.4b virus (H5N6 2.3.4.4b) have been reported to the World Health Organization, with 26 human infections reported in 2021 as of 19 November, all but one reported from China. Most infected persons reported exposure to poultry or poultry environments prior to infection. The majority of infections have resulted in severe illness requiring hospitalization, with 9 deaths in 2021. In addition, surveillance reports indicate detection of A(H5N6) 2.3.4.4b in poultry, waterfowl, and environmental samples.
In 2013, a HPAI A(H5N6) virus was first detected in poultry in China. From 2016-2019, A(H5N6) clade 2.3.4.4b virus was reported in wild birds and in domestic poultry from multiple countries throughout Asia, Europe, and Africa. However, during 2020-2021, A(H5N6) clade 2.3.4.4b virus was only reported in birds in four countries in Asia.
Genetic sequence data from the 2021 human infections suggest that the A(H5N6) 2.3.4.4b viruses remain adapted to poultry, with no evidence of mammalian adaptation or increased transmissibility. Previously recommended H5 candidate vaccine viruses and antivirals are expected to be effective against A(H5N6) viruses currently circulating among poultry. In addition, A(H5N6) virus analysis suggests that they remain susceptible to available influenza antiviral medications.
Summary: A risk assessment of clade 2.3.4.4b, highly pathogenic avian influenza A(H5N6) virus, including a representative virus, A/Sichuan/06681/2021, was conducted in October 2021. The overall estimated IRAT scores placed this virus in the middle range of the moderate risk category, (which ranges from 4.0 to 7.9). The average risk score for the estimated potential emergence of the virus was 5.3, in the middle range of the moderate risk category. The average risk score for the virus to potentially impact public health was 6.3, also in the middle range of the moderate risk category. The average confidence level in the available data of all 10 risk elements was 1.9 (range: 1.0-2.6). Full report here pdf icon[PDF – 571 KB].
The caveat being this risk analysis, along with our updated case counts, is reliant on getting good, timely information out of China.
For now, based on available information, this new iteration of H5N6 ranks 9th on the CDC's list of zoonotic influenza viruses, far below the Chinese Swine-variant EA H1N1 `G4' virus, which is currently viewed as having the highest pandemic potential of any flu virus on their list.
