Infection caused by highly pathogenic avian influenza viruses (HPAIVs) have caused major economic losses in the poultry industry and pose a serious threat to public health. The A/Goose/Guangdong/1/1996 (gs/GD) lineage of H5 HPAIV emerged in China in 1996 and diverged into 10 genetically independent hemagglutinin (HA) clades (0–9) and subclades. The gs/GD lineage of H5 HPAIV has caused outbreaks worldwide, infecting a range of wildlife, poultry, and humans. Clade 2.3.4.4 H5Nx HPAIV containing multiple neuraminidase (NA) subtypes has dominated outbreaks worldwide from 2014 onwards and further divided into subclades 2.3.4.4a–h. Currently, clade 2.3.4.4b H5N1 HPAIV is predominant globally after causing outbreaks in Europe in the fall of 2020 and in Africa, the Americas, Asia, and Antarctica.

During October 2022–March 2023, a total of 16 different genotypes of H5N1 2.3.4.4b HPAIV caused outbreaks in South Korea, including 174 cases in wild birds. Based on the available surveillance data, no new virus incursions have occurred in South Korea during summer and fall 2023. National surveillance for HPAIV began in South Korea in the fall of 2023. We isolated 3 H5N6 HPAIVs from wild bird carcasses found in South Korea during December 2023 (A/Whooper Swan/Korea/23WC075/2023[H5N6], A/Whooper Swan/Korea/23WC116/2023[H5N6], and A/Bean goose/Korea/23WC111/2023[H5N6]) (Appendix Table 1). We conducted next-generation sequencing of the isolates and shared complete genome sequences publicly. We conducted comparative phylogenetic analysis to infer the origin and evolution of the viruses.