Abstract
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.