In May 2022, we observed a substantial die-off of wild migratory waterbirds on Maliy Zhemchuzhniy Island in the Caspian Sea, Russia. The deaths were caused by highly pathogenic avian influenza A(H5N1) clade 2.3.4.4.b virus. Continued surveillance of influenza viruses in wild bird populations is needed to predict virus spread over long distances.
Keywords: Caspian Sea; H5N1; HPAI virus; Maliy Zhemchuzhniy Island; Russia; clade 2.3.4.4.b; highly pathogenic avian influenza; influenza; mass death; outbreak; respiratory infections; viruses; waterbirds; wild birds; zoonoses.