The US beat back bird flu in 2025 – but the battle isn’t over
After starting the year with its first known bird flu death, the US expanded its efforts to contain the virus, which enabled it to end its public health emergency response months later
Millions of chickens have been culled due to the threat of bird flu
Emily Elconin/Bloomberg via Getty Images
The US experienced its first known bird flu deaths this year, igniting concerns that the virus could set off a pandemic in people. Nevertheless, it still reined in the outbreak enough to warrant ending its emergency response – but public health experts warn the battle is far from over.
“It is still a pandemic in [non-human] animals,” says Meghan Davis at Johns Hopkins University in Maryland. “And the virus is no less deadly now than it was before.”
The pathogen behind the vast majority of cases, a subtype of avian influenza called H5N1, first emerged in poultry in China in 1996. It then resurfaced in 2021, devastating global bird populations and spreading to several mammals, including foxes, seals and cats.
H5N1 is poorly adapted to infecting humans and isn’t known to transmit between people. But it still poses a significant threat, having killed almost half of the nearly 1000 people known to have contracted it worldwide since 2003. These fatalities probably represent severe cases, with most milder incidences going unrecorded. Nevertheless, the risk to people exists, and would be even greater if the virus were to evolve the ability to spread from person to person – a scenario that could spark a pandemic, says Davis.
That is why public health experts were alarmed when H5N1 began circulating among dairy cows in the US in March 2024, the first known instance of it infecting dairy cattle. Not only did this put the virus in close proximity to people, particularly farm workers, but it afforded it one of its best opportunities yet to adapt to spread between humans. Each time the pathogen infects a person or another mammal, it has a chance to acquire mutations necessary for human-to-human transmission, says Davis.
H5N1 has since been detected in more than 1080 herds across 19 US states, while also hounding poultry farms. Between February 2022 and mid-December, it sickened at least 1950 flocks nationwide, forcing farms to cull nearly 200 million birds.
The farm outbreaks subsequently fuelled a spike in human cases. Of the who have ever tested positive for bird flu in the US as of December 2025 all but six contracted it from infected dairy cows or poultry. As to those six cases, three contracted it from another animal source, while the origin of the remaining three incidences is a mystery, although there isn’t reason to believe they picked it up from another person.