‘It’s completely out of control’: Scientists warn bird flu could spark a human pandemic in 2026 | BBC Science Focus Magazine

When a highly pathogenic strain of bird flu strain of avian influenza (H5N1) began sweeping across wild birds and poultry in 2020, it already looked concerning. Five years on, the picture has grown darker and stranger than most would have imagined. The virus has infected hundreds of millions of farm animals, spilled into mammals at an unprecedented scale, devastated wildlife, and – in the United States – established itself in dairy cattle, a species no one expected to see implicated. Human cases remain rare. But virologists say the trajectory is troubling, the data patchy and the future uncertain. “It’s now a global problem,” says Dr Ed Hutchinson , professor of molecular and cellular virology at the University of Glasgow. “As a disease of wild animals, it’s completely out of control. It’s raging around the world, and there’s no feasible containment method other than just watching it infect huge populations of animals.” How quickly has the virus spread? The current lineage of H5N1 emerged in Asia in the late 1990s and has since swept from continent to continent. Since 2020, a particularly aggressive branch of the virus – known to scientists as clade 2.3.4.4b – has spread explosively through wild birds. More than 180 million poultry have been infected in the US alone, and over 1,000 dairy farms have reported outbreaks. Egg prices have soared, and the US government has spent more than $1.19bn (£881m) reimbursing farmers for losses. For now, the human toll remains limited: only 71 confirmed cases in the US, resulting in two deaths. Historically, though, H5N1 has been far deadlier: since 2003, almost half of all known human infections globally have proved fatal. Even so, something unprecedented has happened. In early 2024, H5N1 was found in dairy cattle in the United States. “This was to everyone’s astonishment,” Hutchinson says, “You now have a situation where a large proportion of consumer milk in the US at any given time contains genetic material from these highly pathogenic viruses.” Thankfully, pasteurisation destroys the virus. But raw milk, along with close contact for workers on dairy farms, still poses significant risks of infection. Average egg prices in the US peaked at more than $6 (£4.40 approx) per dozen in March 2025 as swathes of flocks of hens were culled due to bird flu infections - Photo credit: Getty That unexpected species jump – along with growing evidence of infection in mammals from seals to foxes to bears – increases opportunities for the virus to change and adapt. Flu viruses are unusually good at evolving because their genome is segmented. If two different strains infect the same host cell, their gene segments can mix and match, producing a new hybrid virus. This process, known as genome reassortment, has played a key role in sparking past pandemics, and many experts are concerned the same could happen if a person infected with a human influenza were also infected with bird flu. This may, for example, allow the virus to gain the ability to transmit...

Preview: ~500 words