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February 4, 2025
Since early 2022, a U.S. H5N1 avian influenza (“bird flu”)
outbreak in poultry and wild birds has led to outbreaks in
dairy herds. Increasing cases of transmission from animals
to humans occurred in 2024. H5N1 influenza is a subtype
of influenza A virus that causes highly pathogenic avian
influenza, a form of influenza that is highly contagious and
deadly to birds. The virus has adapted to spread among
certain mammal species such as cattle and cats. Currently,
H5N1 influenza is not known to spread easily from human
to human. To date, most human H5N1 influenza cases have
been associated with animal exposures, with very few cases
due to human-to-human transmission. Yet many
uncertainties persist around if and when H5N1 influenza
virus might adapt to spread more easily among humans,
potentially resulting in a pandemic. In this case, most
people would not have prior immunity to H5N1 influenza
virus, which means the virus could spread quickly. The
virus’s growing spread among animals creates more
opportunities for a strain with human pandemic potential to
emerge.
continued: https://crsreports.congress.gov/product/pdf/IF/IF12895
Since early 2022, a U.S. H5N1 avian influenza (“bird flu”)
outbreak in poultry and wild birds has led to outbreaks in
dairy herds. Increasing cases of transmission from animals
to humans occurred in 2024. H5N1 influenza is a subtype
of influenza A virus that causes highly pathogenic avian
influenza, a form of influenza that is highly contagious and
deadly to birds. The virus has adapted to spread among
certain mammal species such as cattle and cats. Currently,
H5N1 influenza is not known to spread easily from human
to human. To date, most human H5N1 influenza cases have
been associated with animal exposures, with very few cases
due to human-to-human transmission. Yet many
uncertainties persist around if and when H5N1 influenza
virus might adapt to spread more easily among humans,
potentially resulting in a pandemic. In this case, most
people would not have prior immunity to H5N1 influenza
virus, which means the virus could spread quickly. The
virus’s growing spread among animals creates more
opportunities for a strain with human pandemic potential to
emerge.
continued: https://crsreports.congress.gov/product/pdf/IF/IF12895