Evidence of novel reassortment in clade 2.3.4.4b avian influenza H5N1 viruses, India, 2024

H5N1 viruses belonging to clade 2.3.4.4b have caused unprecedented outbreaks globally. Outbreaks of H5N1 virus were reported in poultry and wild birds from Kerala (India) in the year 2024. Samples from birds and the environment were collected. Real-time RT-PCR and virus isolation using embryonated chicken eggs were carried out. Eight out of 20 samples were positive for virus isolation. The virus showed avian type receptor specificity using sialidase assay. Full genome sequencing revealed markers associated with high pathogenicity and mammalian adaptation. All the viruses belonged to a single genotype with multiple reassortments, including internal gene segments from an avian influenza (AI) H3N8 virus reported from Kerala. Surveillance among individuals with probable exposure showed absence of human infection. This is the first report of the genetic and virological characterization of clade 2.3.4.4b H5N1 viruses from India, highlighting the need for increased AI surveillance at the human-animal and domestic-wild bird interfaces.