Mutation in H5N1 Bird Flu Could Trigger Pandemic in Humans

A new study has raised alarm bells about the potential for the H5N1 bird flu virus to evolve into a strain sparking a human pandemic. A single mutation in the virus currently ravaging dairy farms across the country could significantly enhance its ability to attach to human cells—a critical step for human-to-human transmission—according to the study published in Science. The H5N1 strain has already caused 58 human infections across seven U.S. states in 2024, according to the Centers for Disease Control and Prevention (CDC). Bird flu viruses typically require multiple mutations to adapt to humans, but that might not be the case with this strain. The study revealed that a single amino acid mutation, dubbed Q226L, in the hemagglutinin protein could allow the virus to bind more effectively to receptors in human cells.

This mutation was tested in laboratory settings—no such mutations have been reported in real-world cases—and demonstrated a significant shift in the virus's ability to attach to human-type receptors. "When you think about mutations happening in nature, to get three is statistically really hard," James Paulson, co-senior author of the study, told Newsweek. "But it's orders of magnitude easier to get one. And so that's the red flag that says we really need to keep paying attention to what's going on." H5N1 infections in humans remain rare and have been primarily linked to direct contact with contaminated environments, infected birds, and, most recently, dairy cows. This year alone, 707 dairy herds have been affected, with California reporting the highest number of human cases (32). The spread of the virus in dairy farms is particularly worrying, as these sites have been the source of most human infections. Influenza viruses mutate rapidly to survive, producing millions of variants within a single host. Most mutations are harmless or detrimental to the virus, but those that enhance survival or transmission are naturally selected. "The key is how these mutations are selected for," Paulson said. "If the virus can't survive with that mutation being present, then it's not selected for, and it's never propagated to another person." Historically, avian flu strains have required multiple genetic changes to transmit efficiently between humans. It's uncertain whether this is the case for this bovine strain. "The findings demonstrate how easily this virus could evolve to recognize human-type receptors," the study's first author and a postdoctoral associate at Scripps Research, Ting-Hui Lin, said in a statement. "However, our study doesn't suggest that such evolution has occurred or that the current H5N1 virus with only this mutation would be transmissible between humans." While the findings don't suggest that the current H5N1 virus can spread between humans, they underscore the importance of vigilant monitoring. Paulson is particularly concerned about the upcoming flu season. He explained that farm workers exposed to both human and avian influenza could increase the chance of a hybrid virus emerging—one capable of person-to-person transmission. Another senior author of the study, Ian Wilson echoed the calls for vigilance. "There's got to be a lot of surveillance going on and looking to see whether the viruses are starting to mutate in such a way that they could start to infect humans," Wilson told Newsweek. The study's authors stressed that there is no immediate cause for alarm but urged proactive measures to track H5N1's evolution. "There are lots of factors required for a pandemic to happen," Wilson said. Is there a health problem that's worrying you? Let us know via health@newsweek.com. We can ask experts for advice, and your story could be featured in Newsweek.

Reference

Lin, T.-H., Zhu, X., Wang, S., Zhang, D., McBride, R., Yu, W., Babarinde, S., Paulson, J. C., & Wilson, I. A. (2024). A single mutation in bovine influenza H5N1 hemagglutinin switches specificity to human receptors. Science. https://doi.org/10.1126/science.adt0180