High pathogenicity avian influenza (HPAI) H5N1 clade 2.3.4.4b (hereafter HPAI H5N1) is the cause of a globally devastating animal pandemic (panzootic). Since 2020, HPAI H5N1 has had a substantial range expansion and has now been detected on every continent. In the Antarctic region, the virus was first identified in the sub-Antarctic (South Georgia Island) in October 2023, with the first confirmed detection in the Antarctic Treaty Area (ATA) occurring on the Antarctic Peninsula a few months later. HPAI H5N1 reoccurred in this region in the austral summer of 2024/2025 and 2025/2026. Considerable expansion of HPAI H5N1 in the sub-Antarctic occurred by the austral summer of 2024/2025 with detections on Gough Island, Marion Island, Kerguelen Island and Crozet Islands. In the 2025 austral spring, the virus was also detected on Australia´s sub-Antarctic Heard Island, and in June 2026, this same lineage was confirmed in Australia. To date, spread beyond the Antarctic Peninsula to other parts of continental Antarctica has not been observed.