Pasteurized milk containing H5N1 virus proteins and genetic fragments poses little to no health risk, according to a new study published in Science Advances by scientists at St. Jude Children’s Research Hospital. The findings come as the H5N1 outbreak continues to affect dairy cows across the United States, raising public concerns about milk safety.
The research team set out to answer a critical question: whether repeated exposure to inactivated viral fragments in milk could teach the immune system to ignore influenza proteins — a process known as oral tolerance — and potentially make people more vulnerable to future infections.
Study confirms no change in immune response
In a carefully designed experiment, researchers gave laboratory mice milk contaminated with H5N1 virus that had been pasteurized, as well as uncontaminated pasteurized milk, over several days. Weeks later, both groups of mice were challenged with a live H5N1 infection.
“We found an influenza infection after repeated exposure to H5N1 virus in pasteurized milk was normal, with no adverse events,” said first author Pamela Brigleb, PhD, from the St. Jude Department of Host-Microbe Interactions. “We saw no evidence of it worsening the disease.”
The team further tested whether prior flu exposure — common in human populations through infection or vaccination — affected outcomes. Mice previously infected with a nonlethal H1N1 virus were completely protected against death when later exposed to H5N1, regardless of the type of milk they consumed.
Unpasteurized milk remains a health risk
While pasteurized milk was proven safe, unpasteurized milk contaminated with H5N1 was highly pathogenic. Mice that consumed it died within days, reinforcing the importance of milk pasteurization as a public health safeguard.
“We did see that if infected milk wasn’t fully pasteurized, that was still very pathogenic in our model,” Brigleb said. “That highlights the importance of pasteurization, especially in potentially contaminated milk.”
Implications for public health
These findings are reassuring for consumers and health authorities, confirming that current food safety standards are effectively protecting public health.
