Revised and updated nomenclature for highly pathogenic avian influenza A (H5N1) viruses


  • World Health Organization/World Organisation for Animal Health/Food and Agriculture Organization (WHO/OIE/FAO) H5N1 Evolution Working Group

    Corresponding author
    • Correspondence: Gavin J.D. Smith, Program of Emerging Infectious Diseases, Duke-NUS Graduate Medical School, Singapore 169857, Singapore. E-mail:

      Ruben O. Donis, Influenza Division, Centers for Disease Control and Prevention, MS G16, Atlanta, Georgia 30333, USA. E-mail:

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    • Group members and collaborators are provided in the Supporting Information (Data S1).


The divergence of the hemagglutinin gene of A/goose/Guangdong/1/1996-lineage H5N1 viruses during 2011 and 2012 (807 new sequences collected through December 31, 2012) was analyzed by phylogenetic and p-distance methods to define new clades using the pre-established nomenclature system. Eight new clade designations were recommended based on division of clade 1·1 (Mekong River Delta), 2·1·3·2 (Indonesia), 2·2·2 (India/Bangladesh), 2·2·1·1 (Egypt/Israel), and 2·3·2·1 (Asia). A simplification to the previously defined criteria, which adds a letter rather than number to the right-most digit of fifth-order clades, was proposed to facilitate this and future updates.