Bird flu — specifically H5N1 — is no longer just a poultry problem in Asia. What started as a major United States outbreak first in wildlife, then in poultry, and later in dairy cattle is raising new concerns about food security, the economy, the health of farm workers, and the potential for future human outbreaks.
In commentary published recently in The Journal of Infectious Diseases, Dr. Gregory Gray, a professor in the Division of Infectious Disease and Department of Microbiology and Immunology at The University of Texas Medical Branch (UTMB), writes that vaccinating dairy cattle could be one of the most important steps the U.S. takes to get ahead of this evolving threat
“This virus has changed and now seems to have become entrenched or ‘enzootic’ in North America wildlife,” Gray said. “We used to think of H5N1 as a bird problem in Asia. Now it’s clearly something bigger and here in our own backyard, and we need to respond accordingly. At first, people thought this was a one-off event, but it spread — and it’s still spreading.”
The current wave of H5N1 began sweeping through U.S. poultry flocks in 2022, leading to the loss of more than 190 million birds. By 2024, the virus had made an unexpected jump into dairy cattle.
So far, more than 1,000 dairy herds across at least 19 states have been affected, contributing to an estimated $14 billion hit to the U.S. economy, including roughly $4 billion in losses to the dairy sector alone.
Viruses like H5N1 evolve over time. The more they spread and the more species they infect, the more opportunities they have to change. Dairy cattle may now be acting as what researchers describe as a kind of “training ground” for the virus to adapt to mammals, including humans.
“Every H5N1 infection in animals or humans is like a roll of the dice,” Gray said. “Most of the time, nothing major happens. But the more chances the virus gets, the greater the risk that the virus will become more dangerous to animals or humans.”
So far, human cases in the U.S. have been rare and mostly mild. But there have been at least 71 confirmed infections and two deaths, and public health experts are watching closely. People who work on or live near farms and those who consume raw (unpasteurized) milk may face higher exposure risks.
The idea is straightforward: If you can reduce how much virus is circulating in dairy herds, you reduce the chances of it spreading to other animals, to other farms, and to people.
“Think of it as turning down the volume on the virus,” Gray said. “You may not eliminate it entirely, but you make it much harder for it to cause serious problems.”
Vaccination could help protect cattle from illness, reduce virus levels in milk and on farms, slow or stop spread between herds, and lower the risk of spillover into humans and other species. It could also help protect poultry farms, which are highly vulnerable and often located near dairy operations.
There’s good reason to think vaccines could work well in cattle. Studies show that cows can develop strong, lasting immunity after infection. In some cases, animals remained protected for more than a year and did not shed virus when reexposed.
“That’s exactly what you want to see,” Gray said. “It tells us the immune system in cattle can handle this virus and that vaccines have a real shot at working.”
Early vaccine trials are also promising, with some candidates producing protective immune responses that last for months. Even better, the dairy industry already has the infrastructure to make vaccination practical. Routine vaccinations and detailed herd records are standard practice on most farms.
“This isn’t starting from scratch,” Gray noted. “We already have systems in place that could support a vaccine rollout.”
The idea of vaccinating animals against bird flu isn’t new. Countries like Mexico and China have used vaccines in poultry for years. While vaccination didn’t eliminate the virus, it significantly reduced illness and helped control outbreaks.
“Vaccines don’t have to be perfect to be useful,” Gray said. “If they reduce disease and transmission, that’s a win. We’ve been trying to control this with the tools we have, but it’s becoming clear those tools aren’t enough on their own. The longer we wait, the harder this gets. Right now, we have a chance to get ahead of it.
“This is about staying one step ahead,” Gray said. “We have the science. Now it’s about deciding to use it.”
Additional authors on this commentary are Drs. Cody Warren and Andrew Bowman (The Ohio State University Department of Veterinary Medicine) and Dr. Richard Webby (World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds).