As farmers across the US struggle to contain a deadly bird flu virus, the US Department of Agriculture (USDA) is considering adding animal vaccines to its strategy for controlling the outbreak.
Until now, vaccination was largely off the table given some countries restrict trade on inoculated birds. This includes , one of the largest importers of US poultry products. The concern is that vaccinated flocks can harbour residual amounts of the virus, potentially spreading it to importing countries. Until now, the USDA has relied instead on depopulation, which involves killing all birds on an affected farm and reimbursing farmers for lost profits.
While this approach slowed the spread of bird flu for decades, it hasn’t stopped a highly contagious version of the virus, called H5N1, from decimating US farms. In January, the virus killed birds in commercial and backyard flocks across the US and another 12.6 million in February. As a result, average eggs prices hit a record high in the US last month. The virus also entered dairy cows for the first time last year, infecting at least since March 2024.
Advertisement
Given the urgency of the outbreak, both the dairy and poultry industries have to reconsider vaccines. In response, the agency unveiled a for tackling H5N1 on 26 February. Up to $100 million will go towards developing vaccines and other solutions for preventing the virus’s spread in poultry.
The USDA has already conditionally approved four avian influenza vaccines for birds, meaning they can be used in special circumstances. For instance, one vaccine was used to protect endangered from H5N1 in 2023. The agency said that it will work with states, farmers and public health officials before making a decision on whether to expand approval for use in poultry.
While the new plan is primarily focused on egg-laying chickens, “the $100 million for vaccine and therapeutic developments is not strictly for poultry”, says at the National Milk Producers Federation in Virginia. This suggests it could go towards vaccinating dairy cattle as well, which may also help reduce the spread in chickens. A USDA report in June 2024 found that , potentially through people who work at both or who live with workers from the other type of farm.
The USDA says it has already approved several trials of vaccines designed to protect dairy cattle from H5N1, but it cannot confirm when these trials will end. “My understanding is that there are around 10 or so different vaccine candidates that are in various stages of field trial,” says Jonker.
One H5N1 vaccine, developed by the US biotechnology company Medgene, is in the final stages of review for conditional approval. On 25 February, Elanco Animal Health, a US pharmaceutical company, announced it with Medgene to bring the vaccine to market for use in dairy cattle. Such a vaccine “can slow the virus’s spread, not just supporting our dairy farmer customers, but curbing disease spread for our poultry producers and bringing egg prices down for consumers”, says an Elanco spokesperson.
Unlike poultry, vaccinating dairy cattle is unlikely to affect trade, says Jonker. That is because exported dairy products are pasteurised, which kills the virus.
However, other factors, such as cost and efficacy, will influence whether farmers decide to inoculate dairy cattle against H5N1, says at Johns Hopkins University in Maryland. “I think the market pressures that are really prevalent in poultry are not as prominent in dairy,” she says. “In some herds, it is a very small number of animals that become ill and the long-term impacts to production aren’t well known.”
Still, exploring vaccination for both poultry and dairy cattle is a crucial step towards addressing the outbreak. “We would like vaccines to be in that toolbox and to understand what circumstance can they be used in,” says Jonker. “We think it could be a really powerful tool in the response process.”
