Evolution and Spread of Y280‐Lineage H9N2 Low Pathogenicity Avian Influenza Viruses in Korea, 2020–2023

In 2020, Y280‐lineage H9N2 low pathogenic avian influenza was detected in South Korea for the first time. Active surveillance from live bird markets (LBMs) and farms revealed the continuous circulation of Y280‐lineage H9N2 viruses, replacing the previously indigenous Y439‐lineage and becoming dominant in South Korea. Antigenic mapping showed a substantial antigenic difference between the Y280 and Y439‐lineage viruses. Bayesian phylodynamic approach suggests the introduction of Y280‐lineage viruses from China and revealed the frequent exchange of viruses between LBM and farms. The presence of mammalian adaptation markers and high binding affinity to human‐type sialic acid receptor raise a concern on interspecies transmission of the viruses to mammals. These findings underscore the importance of continued genomic surveillance to monitor the evolution of H9N2 viruses and assessment of zoonotic potential.