US Public Health Preparedness and Response to Highly Pathogenic Avian Influenza A(H5N1) Viruses

Since 2020-2021, highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b viruses have spread among wild birds worldwide, causing poultry outbreaks and spillover to terrestrial and marine mammals. HPAI A(H5N1) clade 2.3.4.4b viruses were first identified in wild birds in North America in late 2021 and continue to evolve and spread. Since February 2022, in the US, HPAI A(H5N1) viruses were detected in wild birds in 49 states, in terrestrial and marine mammals in 27 states, in livestock in a small number of states, and caused outbreaks in commercial poultry or backyard bird flocks in 48 states.