The detection of highly pathogenic avian influenza (HPAI) H5N1 in U.S. dairy cattle in March 2024 prompted an urgent scientific response. Researchers at the Vaccine and Infectious Disease Organization (VIDO) launched a study to determine how the virus affects cows and whether natural immunity could develop. Their findings suggest that dairy cattle can build immunity after initial exposure, reinforcing the potential effectiveness of a vaccine in managing H5N1 outbreaks.
Impact of H5N1 on Dairy Cattle
To date, over 800 U.S. dairy herds have been affected by H5N1, leading to severe mastitis, reduced milk production, and viral shedding in milk. Historically, cattle were believed to be resistant to influenza A viruses, making this discovery a significant shift in scientific understanding. The presence of H5N1 in dairy herds has raised concerns within both agricultural and global health communities due to its potential for further viral evolution.
Key Research Findings
VIDO scientists, using their state-of-the-art Containment Level 3 Agriculture (CL3-Ag) facility, simulated natural infection by introducing the virus into cows’ udders—replicating how contaminated milking equipment might spread the disease. Infected cows exhibited mastitis, reduced milk production, and viral shedding, mirroring real-world outbreaks in the U.S.
The breakthrough came when researchers re-exposed the same cows to the virus in previously unaffected udder quarters. This time, the cows showed no signs of illness. Milk production remained stable, and the virus was undetectable.
This study demonstrates that natural infection can induce immunity, preventing reinfection in other parts of the udder, explained Dr. Antonio Facciuolo, co-lead researcher. This finding strongly indicates that a vaccine would be effective, which is crucial for managing HPAI in dairy cattle.
Why This Discovery Matters
The introduction of H5N1 to cattle creates a new host for the virus, raising concerns about potential mutations. When a virus adapts to a new host, it increases the chances of genetic changes that could lead to new strains, noted Dr. Yan Zhou, co-lead researcher. Cattle could act as a breeding ground for variants that may pose a greater threat to humans.
Understanding that cows can develop immunity opens the door for strategic interventions, including vaccination, to prevent infection, safeguard milk production, and reduce premature culling. This discovery underscores the need for proactive disease management in dairy herds.
Although human cases linked to infected dairy cows are rare, at least 40 have been reported. Ongoing research aims to clarify transmission pathways, including airborne spread, surface contact, and direct exposure.
Next Steps in H5N1 Research
VIDO continues to investigate how natural immunity provides protection in the mammary gland. These insights could lead to vaccines or other preventive measures to protect dairy herds. The organization is also collaborating with the Research Alliance for Veterinary Science and Biodefense (RAV3N) to advance response strategies for this emerging infectious disease.
If we can pinpoint the mechanisms behind this immune response, we could revolutionize how we protect both animals and humans from H5N1, said Dr. Bryce Warner, another co-lead researcher.
This research highlights the importance of a One Health approach—integrating human, animal, and environmental health perspectives to combat zoonotic diseases.
VIDO is uniquely positioned to conduct this level of research, emphasizing the link between human and animal health, said Dr. Volker Gerdts, Director and CEO of VIDO. By understanding how H5N1 behaves in cattle, we can better protect herds, ensure food security, and mitigate future pandemic risks.
For those interested in further details, the full research findings are available in the published study.
