We report 4 highly pathogenic avian influenza A(H5N1) clade 2.3.4.4.b viruses in samples collected during June 2023 from Royal terns and Cabot's terns in Brazil. Phylodynamic analysis revealed viral movement from Peru to Brazil, indicating a concerning spread of this clade along the Atlantic Americas migratory bird flyway.
Keywords: Brazil; H5N1; highly pathogenic avian influenza virus; influenza; phylodynamic analysis; phylogenetic analysis; respiratory infections; viruses; wild bird; zoonoses.