Genetically Divergent Highly Pathogenic Avian Influenza A(H5N8) Viruses in Wild Birds, Eastern China

H ighly pathogenic avian infl uenza (HPAI) A(H5Nx) clade 2.3.4.4 viruses, which originated from the HPAI A(H5N1) clade 2.3.4 of the A/ Goose/Guangdong/1/96-lineage in China, have spread globally, causing severe disease in poultry and wild birds (1-4). According to the World Health Organization, clade 2.3.4.4 viruses have evolved into 8 subclades, designated as clades 2.3.4.4a-h (https://www.who.int/influenza/vaccines/virus/202002_zoonotic_vaccinevirusupdate.pdf). In 2013, a novel reassortant A(H5N8) clade 2.3.4.4b virus was isolated from domestic ducks in eastern China (2); this virus was later detected in Korea and Japan (3). Since 2014, clade 2.3.4.4b viruses have spread to Europe and Africa along the migratory fl yways of birds (4,5). These introductions caused large HPAI outbreaks in wild and domestic birds in Europe during the winter of 2016-17 (6). At the same time, wild birds carried clade 2.3.4.4c viruses to North America (4).