Mammalian infections with highly pathogenic avian influenza viruses renew concerns of pandemic potential.

There is unprecedented spread of highly pathogenic avian influenza A H5N1 viruses in bird species on five continents, and many reports of infections in mammals most likely resulting from consumption of infected birds. As H5N1 viruses infect more species, their geographical range increases and more viral variants are produced that could have new biological properties including adaptation to mammals and potentially to humans. This highlights the need to continually monitor and assess mammalian-origin H5N1 clade 2.3.4.4b viruses for the presence of mutations that could potentially increase their pandemic risk for humans. Fortunately, to date there have been a limited number of human cases, but infection of mammals increases the opportunity for the virus to acquire mutations that enhance efficient infection, replication, and spread in mammals, properties that have not been seen in these viruses in the past.