Cross-species and mammal-to-mammal transmission of clade 2.3.4.4b highly pathogenic avian influenza A/H5N1 with PB2 adaptations

Highly pathogenic H5N1 avian influenza lineage 2.3.4.4b has spread through the Americas in birds since 2021 with frequent spillover into mammals. Here, the authors characterise the dissemination of the virus in Chile and find evidence of sustained transmission between mammals.