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Updated joint FAO/WHO/WOAH assessment of recent influenza A(H5N1) virus events in animals and people (Assessment based on data as of 18 July 2024)

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Key points

At the present time, based on available information, FAO-WHO-WOAH assess the global public health risk of influenza A(H5N1) viruses to be low, while the risk of infection for occupationally exposed persons is low to moderate depending on the risk mitigation measures in place. Transmission between animals continues to occur and, to date, a limited number of human infections have been reported. Although additional human infections associated with exposure to infected animals or contaminated environments are likely to continue to occur, the overall public health impact of such infections at a global level is minor.

Background

During 2020, high pathogenicity avian influenza (HPAI) A(H5N1) clade 2.3.4.4b viruses arose from previously circulating influenza A(H5Nx) viruses and spread predominantly via migratory birds to many parts of Africa, Asia and Europe. This epizootic event has led to unprecedented numbers of deaths in wild birds and caused outbreaks in poultry. In late 2021, these viruses crossed the Atlantic Ocean to North America and subsequently reached South America in October 2022. Over the past few years, there have been increased detections of A(H5N1) viruses in non-avian species globally including wild and domestic (companion and farmed) terrestrial and marine mammals, with recent cases in livestock in the United States of America (USA). The majority of A(H5N1) viruses characterized genetically since 2020 belong to the haemagglutinin (HA) H5 clade 2.3.4.4b, with some regional exceptions. Other circulating A(H5N1) viruses belong to clade 2.3.2.1a or 2.3.2.1c or fall within clades that are reported less frequently. Since the beginning of 2021, 35 detections of A(H5N1) virus in humans have been reported to WHO, along with five cases of A(H5) virus detection in persons exposed to A(H5N1) infected animals, presumably A(H5N1) viruses, although the neuraminidase (NA) subtype was unable to be determined due to low viral ribonucleic acid (RNA) loads. Of these human cases where the A(H5) clade is known (n = 31), 17 have been caused by clade 2.3.4.4b viruses.

Considering additional information made available since the previous assessment of 23 April 2024, FAO, WHO, and WOAH jointly updated their assessment here. This update focuses on A(H5N1) viruses characterized since 2021 and covers the risk of zoonotic transmission. Due to the potential risk to human health and the far-reaching implications of the disease on the health of wild bird and other animal populations, using a One Health approach is essential to tackle avian influenza effectively