Pandemic potential of highly pathogenic avian influenza clade 2.3.4.4 A (H5) viruses

Authors: YAMAJI, REINA - World Health Organization (WHO) - Switzerland; SAAD, MAGDI - World Health Organization (WHO) - Switzerland; DAVIS, CHARLES - Centers For Disease Control And Prevention (CDC) - United States; Swayne, David; WANG, DAYAN - Chinese Center For Disease Control; WONG, FRANK - Australian Animal Health; MCCAULEY, JOHN - The Francis Crick Institute; PEIRIS, J S MALIK - University Of Hong Kong; WEBBY, RICHARD - St Jude Children’s Research Hospital; FOUCHIER, RON - Erasmus Medical Center; KAWAOKA, YOSHIHIRO - University Of Tokyo; ZHANG, WENQING - World Health Organization (WHO) - Switzerland

Submitted to: Reviews in Medical Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2020
Publication Date: 3/5/2020
Citation: Yamaji, R., Saad, M.D., Davis, C.T., Swayne, D.E., Wang, D., Wong, F.Y., Mccauley, J.W., Peiris, J., Webby, R.J., Fouchier, R.A., Kawaoka, Y., Zhang, W. 2020. Pandemic potential of highly pathogenic avian influenza clade 2.3.4.4 A (H5) viruses. Reviews in Medical Virology. 30:1-16. https://doi.org/10.1002/rmv.2099.
DOI: https://doi.org/10.1002/rmv.2099

Interpretive Summary: The H5N1highly pathogenic avian influenza (HPAI) viruses from Eurasia have caused sporadic human infections since 1997 in Asia and Africa. A new group of these viruses called Clade 2.3.4.4 have been distributed via long distance migratory bird onto several continents and through poultry trade among neighboring countries. These viruses have caused only sporadic human infections and lack the ability for transmission between humans. However, some 2.3.4.4 viruses transmit between ferrets in direct contact and have molecular signatures related to mammalian adaptation. This calls for surveillance of influenza viruses in domestic and wild birds to be expanded and fully integrated with laboratory and field-based risk assessment to allow for development and updated veterinary and public health countermeasures to reduce the threats of zoonotic and pandemic influenza.

Technical Abstract: The panzootic caused by A/goose/Guangdong/1/96-lineage highly pathogenic avian influenza (HPAI) A(H5) viruses has occurred in multiple waves since 1996. From 2013 onwards, clade 2.3.4.4 viruses of subtypes A(H5N6), A(H5N2) and A(H5N8) emerged to cause panzootic waves of unprecedented magnitude among avian species accompanied by severe losses to the poultry industry around the world. Clade 2.3.4.4 viruses have expanded in distinct geographical and evolutionary pathways likely via long distance migratory bird dispersal onto several continents and by poultry trade among neighboring countries. As regional circulation has proceeded, the viruses have evolved further by reassorting with local viruses. As of February 2019, there have been 23 cases of humans infected by clade 2.3.4.4 H5N6 virus, 16 (70%) of which had fatal outcomes. To date, no HPAI A(H5) virus has caused sustainable human-to-human transmission. However, due to the lack of population immunity in humans and ongoing evolution of the virus, there remains a possibility that clade 2.3.4.4 viruses could cause an influenza pandemic if the ability to transmit efficiently among humans was gained. Therefore, multisectoral collaborations between the animal, environmental and public health sectors under the “One Health” concept should continue in order to develop countermeasures to prevent disease and control spread. In this manuscript, we describe an assessment of the likelihood of emergence in humans and impact on human health should clade 2.3.4.4 viruses gain human-to-human transmissibility. This structured analysis assessed properties of the virus, attributes of the human population, and ecology and epidemiology of these viruses in animal hosts.