H5N1 in dairy cattle roundup: New research highlights airborne transmission risks and a promising dual-route vaccine

Two newly published studies are adding urgency and nuance to the H5N1 story in US dairy herds—one mapping the virus’s previously underappreciated transmission routes on California farms, the other offering a first look at a dual-route vaccine platform that achieved complete protection in preclinical bovine models.

A detailed look at how H5N1 spreads on dairy farms

A study published May 5, 2026, in PLOS Biology offers some of the most detailed field evidence yet that H5N1 spreads on dairy farms through routes well beyond contaminated milk.

Researchers from Emory University School of Medicine and Colorado State University sampled air, wastewater, and milk across 14 H5N1-positive farms in 2 California regions between October 2024 and January 2025.

The findings were striking: infectious virus was detectable in the exhaled breath of infected cows and in dairy parlor air, as well as in farm wastewater. Equally notable was the high prevalence of cows that tested positive for H5N1 but showed no clinical signs of infection.

“Our data confirm the presence of infectious H5N1 virus in the air and reclaimed farm wastewater sites,” said senior author Seema S. Lakdawala, PhD, of Emory University, in a news release. “In addition, we observed high viral loads and H5 antibodies in the milk of cows, including those without clinical signs, suggesting that multiple modes of H5N1 transmission likely exist on farms.”

The authors noted that the detection of infectious virus in air and waste streams “was surprising but highlights that there is a considerable amount of infectious virus on farms and multiple sources of infection exist.” They recommend targeted interventions in dairy parlors to reduce aerosol load and inactivation of milk from sick animals prior to disposal as additional protective barriers for farm workers and other animals.

The study was limited to 14 farms, and longitudinal sampling of individual cows was restricted to 14 animals, so larger and longer-duration studies are needed to validate the findings. Still, the environmental contamination data point clearly toward a more complex transmission picture than milking-line exposure alone—one with meaningful implications for herd biosecurity protocols and farm worker safety.

California has reported H5N1 in more than 700 dairy herds, making it the most heavily affected state in the country and the site of the most sustained cattle-to-human exposure risk documented to date.

A dual-route vaccine shows preclinical promise in cattle

On the prevention side, researchers at the University of Nebraska–Lincoln have published results in npj Vaccines describing a vaccine platform designed to generate both systemic and mucosal immunity against H5N1 in multiple species. The research was led by Eric Weaver, PhD, professor of biological sciences and director of the Nebraska Center for Virology, with postdoctoral fellows Joshua Wiggins and Adthakorn Madapong.

The vaccine was administered via a combination of intramuscular and intranasal delivery—a dual-route strategy designed to address 2 distinct concerns. Intramuscular vaccination aimed to prevent systemic viral spread within an individual animal; intranasal delivery targeted the mucosal surface to reduce animal-to-animal transmission. Dairy calves received the primary vaccination at one week of age, followed by a booster 4 weeks later.

In separate mouse experiments, vaccinated animals were completely protected against lethal infection across multiple H5N1 strains. There are currently no licensed H5N1 vaccines for cattle, and Weaver is now seeking funding and industry partnerships to advance the platform toward multispecies evaluation.

“The idea was that if we put it intramuscularly, we can prevent it from spreading in the body, and then a mucosal aspect, intranasally, would prevent it from spreading from animal to animal,” Weaver said in a news release. “We’d like to have a vaccine for the farm and the farmer, and everything shows that this would be an effective vaccine platform for humans as well.”

Weaver noted that he began working on H5N1 as a potential problem as far back as 2005 but paused the work a decade ago. When bovine cases began mounting in 2024, he restarted the research program. “Historically, these things will move into other species if there is extended contact long enough for the evolution to occur,” he said. “Influenza A viruses have never been an issue in cattle, but it is now, and it’s not going away.”

What this means for veterinary practice

Together, these studies underscore both the scale of the ongoing H5N1 threat to US dairy cattle and the genuine scientific momentum building around countermeasures. For large animal and mixed-practice veterinarians, the California transmission data reinforce several evidence-based talking points for producer conversations:

• Asymptomatic H5N1-positive cows are a real and measurable phenomenon. Absence of clinical signs does not rule out active infection or shedding.
• Airborne viral exposure in dairy parlors represents an underappreciated risk for farm workers, peridomestic wildlife, and susceptible herd members. Ventilation and aerosol-reduction measures warrant reassessment.
• Wastewater from H5N1-positive farms is a potential vector, with implications for how sick milk is handled and how farm drainage is managed.

The Nebraska vaccine work is preclinical, and a licensed bovine H5N1 product remains years away. But the dual-route approach addresses a recognized gap: conventional IM-only vaccination strategies may limit systemic disease while leaving respiratory shedding insufficiently controlled. A platform that induces both systemic and mucosal immunity could meaningfully reduce within-herd spread if it advances through regulatory review.

References

1. Campbell AJ, Shephard M, Paulos AP, et al. Surveillance on California dairy farms reveals multiple possible sources of H5N1 influenza virus transmission. PLoS Biol. 2026;24(5):e3003761. doi:10.1371/journal.pbio.3003761
2. Wiggins J, Madapong A, Weaver EA. Dual-route H5N1 vaccination induces systemic and mucosal immunity in murine and bovine models. npj Vaccines. Published April 21, 2026. doi:10.1038/s41541-026-01460-6