What you need to know
- On February 10, 2025, the US Centers for Disease Control and Prevention (CDC) released data showing the new D1.1 genotype of avian influenza H5N1 had infected 15 people in five states, including in Nevada, where D1.1 was only recently detected in dairy cattle
- The CDC believes the risk to humans remains low
- Infections have also been detected outside the US, in the United Kingdom
- European authorities are monitoring the North American outbreak
US authorities have said the detection of a different strain of avian influenza, the D1.1 genotype, in dairy cows in January proves that bird flu has now spread from wild birds into cattle twice in an outbreak that started in late 2023.
The genotype refers to the genetic makeup of a virus within a group of virus types. In this case, it is the highly pathogenic avian influenza (HPAI) A H5N1.
In March 2024, authorities in the US confirmed the outbreak had originated from genotype B3.13. That type has infected over 950 cattle herds in 16 US states and spread to Canada.
D1.1 was detected in milk collected as part of a surveillance program launched in December 2024.
Is the bird flu spreading internationally?
Yes, it appears that bird flu from the current US outbreak may have spread beyond North America.
In January, UK authorities confirmed a second human case of H5N1 avian influenza. The first was detected in 2022, the UK Health Security Agency (UKHSA) said.
“The risk of avian flu to the public remains very low despite this confirmed case,” said Susan Hopkins, chief medical adviser at the UKHSA, in a statement on January 27.
However, many governments have been buying up vaccine stocks and ramping up precautionary measures in response to the circulating virus.
The bird flu variant outbreak has mainly affected the US, with infections among cattle, people and pets.
Though no direct, human-to-human transmission cases were recorded up to January 2025, there are concerns the H5N1 variant could be one mutation away from becoming a major public health concern.
A study published in the journal Science in December 2024 found that a single genetic change to the circulating H5N1 had enabled it to jump more easily from other mammals to humans.
“We’re particularly worried about pigs because we know from many other outbreaks that pigs are a mixing vessel for influenza viruses,” Meghan Davis, an environmental health researcher at Johns Hopkins Bloomberg School of Public Health, told DW’s Science Unscripted podcast.
Is a new pandemic brewing?
Before the outbreak of SARS-CoV-2, the virus that causes COVID-19, health scientists warned there was a risk of an emerging pandemic.
Ultimately, it was a novel coronavirus, not an influenza strain, that triggered the pandemic. But the chance of a global influenza-driven event was — and is — cause for concern.
“With H5N1, there’s a big unknown,” Peter Jay Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine in the US state of Texas, told Science Unscripted.
“We know there’s a likelihood that there could be a significant bird flu pandemic, maybe resembling the 1918 flu pandemic,” Hotez said, “but we can’t say when that will be.”
Other nations are increasing surveillance and precautionary measures. The UK government is known to have ordered at least 5 million doses of an H5 influenza vaccine. In November 2024, one case of H5N1 was confirmed at a poultry farm in Cornwall, in the southwest of England.
“I agree with what the UK did because it’s not like you can press a button and suddenly have millions of doses of [H5 vaccine] appear,” Hotez said. “Making flu vaccines in the traditional way is a slow process.”
Hotez described the rate of pandemic threats as having a “regular cadence,” pointing to SARS in 2002 and MERS in 2012, which were dangerous but did not balloon to a global scale.
A pandemic was declared due to H1N1 influenza in 2009, though its impact didn’t match that of COVID-19.
“We have to get ready for H5N1. We’ve also got this rise in Ebola and other filovirus [severe hemorrhagic] infections that we’re seeing — we have to be ready for that,” Hotez said. “And we’re starting to see [a rise in] mosquito-transmitted virus infections like dengue and chikungunya and then Zika virus infections both in Southern Europe and the southern United States.”
Trump‘s health advisers are ‘contrarians, activists’
Scientists and health experts in the United States have expressed concern about several choices that President Donald Trump has made for his new administration.
Among Trump’s picks are Robert F. Kennedy Jr. to lead the Department of Health and Human Services and Dave Weldon for the top job of the Centers for Disease Control and Prevention.
Kennedy and Weldon are known for their opposition to vaccination.
Although Trump was president at the outset of the COVID pandemic and led massive investments in vaccine supply security through programs such as Operation Warp Speed, Hotez said the absence of people with established experience in health issues in Trump’s new administration is concerning.
“[In Trump’s first administration] they were pretty mainstream public health physicians and public health scientists, but this new round is something that’s quite different — they’re contrarians, they’re activists, they’ve openly campaigned against vaccines and interventions,” Hotez said.
Health experts in other nations are closely watching how H5N1 is handled in North America.
“The current incidence of infection in the US demands we closely study samples of viruses from humans and other animals,” said Martin Schwemmle, a virologist at Freiburg University Medical Center.
The European Centre for Disease Prevention and Control said in a November 2024 report that it was continuing to monitor the US and Canadian situations “together with partner organizations in Europe and will continue to update its assessment of the risk for humans … as new information becomes available.”
It also recommended increased surveillance and monitoring of people exposed to avian influenza and that doctors and nurses ask patients whether they have had any contact with animals.