The World Health Organisation says it is concerned about the spread of H5N1 bird flu, which has an “extraordinarily high” mortality rate in humans, and was a virus “just looking for new, novel hosts”.
An outbreak that began in 2020 has led to the deaths or killing of tens of millions of poultry, and most recently, the spread of the virus within several mammal species, including in domestic cattle in the US, has increased the risk of spillover to humans.
Cows and goats joined the list of species affected last month – surprising experts because they were not thought susceptible to this type of influenza – and this month, US authorities reported a person in Texas was recovering from bird flu after being exposed to dairy cattle, with 16 herds across six states infected apparently after exposure to wild birds.
The A(H5N1) variant has become “a global zoonotic animal pandemic”, said the UN health agency’s chief scientist Jeremy Farrar.
“The great concern of course is that in … infecting ducks and chickens and then increasingly mammals, that virus now evolves and develops the ability to infect humans and then critically, the ability to go from human to human.”
The Guardian reports that so far, there is no evidence that H5N1 is spreading between humans. But in the hundreds of cases where humans have been infected through contact with animals over the past 20 years, “the mortality rate is extraordinarily high”, Farrar said, because humans have no natural immunity to the virus.
Between 2003 and 2024, 889 cases and 463 deaths caused by H5N1 have been reported worldwide from 23 countries, putting the case fatality rate at 52%.
The recent US case of human infection after contact with an infected mammal highlights the increased risk. “When you come into the mammalian population, then you’re getting closer to humans,” Farrar said, warning that “this virus is just looking for new, novel hosts”.
Farrar called for increased monitoring, saying it was “very important understanding how many human infections are happening … because that’s where adaptation [of the virus] will happen”.
“If I get infected with H5N1 and I die, that’s the end of it,” he said. “But if I go around the community and spread it to somebody else then you start the cycle.”
He said efforts were under way towards the development of vaccines and therapeutics for H5N1, and stressed the need to ensure that regional and national health authorities worldwide had the capacity to diagnose the virus.
This was so that “if H5N1 did come across to humans, with human-to-human transmission, the world would be in a position to immediately respond”, he added, calling for equitable access to vaccines, therapeutics and diagnostics.
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