Bird flu jumping to humans is ‘enormous concern’, says WHO

National Trust rangers clearing deceased birds from Staple Island, one of the Outer Group of the Farne Islands, off the coast of Northumberland
The H5N1 strain has killed tens of millions of birds worldwide since 2020 - Owen Humphreys/PA Wire

The risk of bird flu jumping into humans is of “enormous concern,” the World Health Organization has warned as the virus continues its spread into new species.

Since 2020, an outbreak of the H5N1 strain has killed tens of millions of birds worldwide, along with thousands of mammals, including sea lions, elephant seals and even one polar bear.

More recently, the virus emerged in 16 herds of cattle in Texas – a development which has surprised experts, as it was previously believed the animals were not susceptible to infection, and raised concerns that H5N1 could eventually spill over into humans.

“This remains, I think, an enormous concern,” Dr Jeremy Farrar, the WHO’s chief scientist, told reporters on Thursday in Geneva.

“When you come into the mammalian population, then you’re getting closer to humans … this virus is just looking for new, novel hosts.”

He warned that, by circulating in new mammals, the virus improves its chances of further evolving and developing “the ability to infect humans and then critically the ability to go from human to human”.

In the recent cattle outbreak in Texas, one person was diagnosed with bird flu following close contact with dairy cows presumed to have been infected.

Over the past 20 years, hundreds of others have caught the virus following exposure to an infected animal – yet there has been no evidence of human-to-human transmission in these cases.

Yet the mortality rate for humans is “extraordinarily high,” Dr Farrar warned.

From 2003 to 2024, 463 deaths and 889 cases were reported from 23 countries, according to the WHO – a case fatality rate of 52 per cent.

The Texas infection is the second case of bird flu in the US and appears to have been the first infection of the H5N1 strain through contact with an infected mammal, said the WHO.

Dr Farrar said the ongoing bird flu outbreak had become “a global zoonotic animal pandemic” and called for increased monitoring, adding that it was “very important” to understand how many human infections are occuring “because that’s where adaptation [of the virus] will happen”.

He added: “It’s a tragic thing to say, but if I get infected with H5N1 and I die, that’s the end of it. If I go around the community and I spread it to somebody else then you start the cycle.”

He said efforts were being made to develop vaccines and therapeutics for the strain and stressed the importance of international health authorities having the capacity to diagnose the virus.

This would ensure that the world would be “in a position to immediately respond” if the strain “did come across to humans, with human-to-human transmission”, said Dr Farrar.

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