Avian Influenza A(H5N5)- United States of America

Human infections with avian influenza A(H5) viruses are considered unusual, as A(H5) viruses remain primarily avian influenza viruses. However, in rare cases, individuals exposed to infected animals or contaminated environments can become infected with A(H5) viruses. Influenza A(H5N5) viruses are detected in birds, including wild birds and domestic poultry, and sometimes in non-human mammals. When avian influenza viruses circulate in poultry populations, there is an inherent risk of human infection through exposure to infected birds or contaminated environments. As such, sporadic human cases are expected. The case had underlying conditions and subsequently died. The investigation by health authorities in the United States of America is ongoing and included contact tracing which identified no further cases amongst contacts, and there is currently no evidence of human-to-human transmission.

This is the 71st confirmed human case of A(H5) in the United States of America since early 2024, and the first since February 2025. To date, no human-to-human transmission has been identified in any of the A(H5) cases reported in the United States of America. From a global perspective, while a few events with limited human-to-human transmission of zoonotic influenza A(H5) have been described between 1997 and 2007, sustained human-to-human transmission has not been detected to date.

Based on available information, the WHO currently assesses the overall public health risk posed by A(H5) viruses as low. However, for individuals with occupational risk of exposure, the risk of infection is considered low to moderate.

The risk assessment will be updated as needed, based on any new epidemiological or virological information related to this event.