Summary Points
Eight Holstein cows received two intramuscular H5N1 mRNA-LNP vaccine doses three weeks apart.
At day 49, researchers challenged two udder quarters with H5N1 and monitored clinical outcomes.
Blood, milk, and other samples assessed antibodies, viral RNA, production, rumination, and mammary damage.
Vaccine mRNA was undetectable in milk; vaccinated cows’ milk was excluded from the food supply.
A promising test in dairy cows
An experimental mRNA vaccine protected lactating cows from H5N1 infection, according to the study. It used lipid particles to carry instructions for making a flu-virus protein. The immune system could then learn to recognize that protein.
Researchers tested the vaccine in eight Holstein cows. Some received two doses, three weeks apart; others received saline. Seven weeks after the first dose, the cows were exposed to H5N1 in two udder quarters. The team tracked milk production, behavior and signs of illness.
Why milk safety matters
The researchers tested milk for vaccine mRNA after vaccination and reported that none was detected. During the study, vaccinated cows were milked separately, and their milk did not enter the human food supply. That precaution matters: the result is reassuring, but it is not a substitute for broader food-safety testing.
Promise, with limits
Protecting cows could help reduce illness on farms and limit disruption to milk production. It may also strengthen efforts to manage a virus that affects both animals and people. Still, eight animals make this an early, small study—not proof of how well the vaccine will work across herds in everyday conditions. Larger studies can show how durable the protection is and whether it holds under field conditions.
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