H5N1 Influenza Virus in Pasteurized Milk Presents Minimal Health Risks

Newswise — (MEMPHIS, Tenn. – September 26, 2025) Proteins and genetic material from H5N1 influenza viruses have been found in pasteurized milk in the United States, but a study from St. Jude Children’s Research Hospital shows those inactive viral pieces represent little to no health risk. As the H5N1 outbreak in dairy cows continues in the U.S., commercial milk remains contaminated by viral pieces. However, the pasteurization process kills the virus. The researchers tested whether the resulting noninfectious viral materials could teach the immune system that these viral components were harmless, thus increasing susceptibility to influenza infections. They found that H5N1-contaminated milk that was pasteurized did not significantly affect the immune system in laboratory models. Unpasteurized milk remains a health concern. The findings were published today in Science Advances.

“We found that consuming pasteurized milk multiple times, even if it has inactivated H5N1 virus, poses minimal health risks,” said corresponding author Stacey Schultz-CherryPhD, St. Jude Department of Host-Microbe Interactions. “We observed no benefit or detriment to subsequent influenza infection.”

The scientists were originally concerned that regularly drinking inactivated viral components in milk may teach the immune system that these molecules were safe. This loss of immunity against materials in food is called oral tolerance, which prevents humans from developing unwanted immune reactions against what they consume. However, if people gained oral tolerance to flu’s viral proteins, it could lead to greater susceptibility to later influenza infections if the body no longer recognizes the viral components as part of an invader.

To learn if drinking contaminated pasteurized milk created oral tolerance of influenza viruses, the researchers took uncontaminated milk or milk contaminated with H5N1, which were both then pasteurized, and gave them to mice. The mice were given the milk over five days, mimicking how a person would consume it over time. Weeks later, the scientists challenged the mice with an H5N1 infection. There was no difference in how the infection proceeded between the two groups.

“We found an influenza infection after repeated exposure to H5N1 virus in pasteurized milk was normal, with no adverse events,” said first author Pamela BriglebPhD, St. Jude Department of Host-Microbe Interactions. “We saw no evidence of it worsening the disease.”

Pasteurization and pre-existing immunity prevent pathogenic infections

While pasteurized milk appeared to play no role in altering influenza immunity, unpasteurized milk represented a health threat. Mice exposed to unpasteurized H5N1-infected milk succumbed to their disease in a matter of days, which other groups have also documented.

“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.”

Until this point, the researchers had only used mice that never had the virus. To better account for pre-existing flu immunity from previous infections and vaccinations, as occurs in the human population, the scientists infected mice with a nonlethal dose of H1N1 virus, leaving another group uninfected. They then took regular milk or milk that was H5N1-infected, then pasteurized both, and gave it to the mice for several days. Weeks later, they challenged those mice with the H5N1 virus, finding that prior H1N1 infection was 100% protective against mortality regardless of what type of milk the mice drank. All mice that did not have the pre-existing H1N1 immunity succumbed to their disease.

“Most of the population has had an infection or a vaccination at some point in their life, so we wanted to reflect that in our experiments,” Brigleb said. “We found that whether or not mice received viral particles in pasteurized milk or not, prior immunity still fully protected them from the H5N1 challenge.”

The study confirms that current food safety methods and vaccination practices are likely protecting human health from the H5N1 virus in milk, though the need for continued vigilance remains.

“It’s reassuring to find that these inactivated H5N1 viral components in pasteurized milk present minimal health risks and don’t alter flu immunity,” Schultz-Cherry said. “However, we also reaffirmed that consuming unpasteurized milk can expose people to this potentially dangerous infectious agent. We must continue to watch this virus and mitigate its risk of spilling over into the human population.”

Authors and funding

The study’s other authors are Ericka Kirkpatrick Roubidoux, Lauren Lazure, Brandi Livingston, Victoria Meliopoulos, Bridgett Sharp, Tyler Ripperger, Shelby Patrick, Dorothea Morris and Shaoyuan Tan, all of St. Jude.

The study was supported by grants from the National Institute of Allergy and Infectious Diseases (Contract No. 75N93021C00016, the National Institutes of Health (T32AI106700-08 and F32AI183804) and ALSAC, the fundraising and awareness organization of St. Jude.

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St. Jude Children’s Research Hospital

St. Jude Children’s Research Hospital is leading the way the world understands, treats, and cures childhood catastrophic diseases. From cancer to life-threatening blood disorders, neurological conditions, and infectious diseases, St. Jude is dedicated to advancing cures and means of prevention through groundbreaking research and compassionate care. Through global collaborations and innovative science, St. Jude is working to ensure that every child, everywhere, has the best chance at a healthy future.  To learn more, visit stjude.org, read St. Jude Progress, a digital magazine, and follow St. Jude on social media at @stjuderesearch.

What specific temperature and time combination is commonly used in High-Temperature Short-Time (HTST) pasteurization to inactivate viruses like H5N1?

Understanding the H5N1 Threat & Dairy Safety

recent detections of the H5N1 influenza virus in dairy cattle have understandably raised concerns about the safety of milk and dairy products. However, it’s crucial to understand that the risk to human health from consuming pasteurized milk is considered minimal. This article, brought to you by archyde.com, will delve into the science behind this, addressing concerns about avian flu, milk safety, and the effectiveness of pasteurization. We’ll cover everything from viral inactivation to current recommendations from health organizations. Keywords: H5N1,avian flu,pasteurized milk,milk safety,influenza virus,dairy safety,bird flu.

The Science of Pasteurization & Viral Inactivation

Pasteurization is a heat treatment process designed to kill harmful microorganisms in milk, including bacteria, viruses, and parasites. The standard process involves heating milk to a specific temperature for a set period, effectively eliminating pathogens without significantly altering the milk’s nutritional value.

Here’s how pasteurization tackles viruses like H5N1:

* Heat Sensitivity: Influenza viruses, including H5N1, are relatively heat-sensitive.

* Temperature & Time: The temperatures used in pasteurization (typically 161°F/72°C for 15 seconds in High-Temperature Short-time – HTST – pasteurization) are sufficient to inactivate the virus. Ultra-High Temperature (UHT) processing, which heats milk to higher temperatures for a shorter duration, provides even greater assurance of viral inactivation.

* Viral Structure Disruption: Heat disrupts the virus’s protein structure, rendering it unable to infect cells. This process effectively neutralizes the avian influenza virus.

Current Findings & Risk Assessment – H5N1 in Dairy

The recent H5N1 outbreaks in dairy cattle have primarily been detected through routine surveillance testing. While the virus has been found in raw milk samples from infected cows, the key takeaway is the effectiveness of pasteurization.

* Raw Milk Risks: Consuming raw, unpasteurized milk from infected animals carries a higher risk of exposure to H5N1. Raw milk bypasses the crucial safety step of heat treatment.

* Pasteurized Milk Safety: To date, no cases of human infection with H5N1 have been directly linked to the consumption of commercially pasteurized milk.

* CDC & FDA Guidance: The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) have consistently stated that the commercial milk supply remains safe due to pasteurization. They continue to monitor the situation closely. Keywords: CDC, FDA, raw milk, commercial milk supply, avian flu risk.

Understanding the Transmission Pathways of H5N1

While the risk from pasteurized milk is low, it’s important to understand how H5N1 spreads:

1. Bird-to-Bird Transmission: Primarily spreads among wild birds and poultry.
2. Mammalian Transmission: Recent outbreaks demonstrate limited mammal-to-mammal transmission (e.g., cattle-to-cattle).
3. Human Infection (Rare): Human infections are rare and typically occur through direct contact with infected birds or animals. The current cases in the US have been linked to close contact with infected dairy cows.
4. Respiratory Droplets: The virus spreads through respiratory droplets produced when infected animals cough, sneeze, or talk.

Benefits of Pasteurization Beyond H5N1 Protection

Pasteurization offers a broad spectrum of health benefits, extending far beyond protection from H5N1:

* Elimination of Harmful Bacteria: Kills bacteria like E. coli, Salmonella, Listeria, and Campylobacter, which can cause severe foodborne illnesses.

* Extended Shelf Life: Increases the shelf life of milk, reducing waste.

* Nutritional Preservation: While some minor nutrient changes occur, pasteurization generally preserves the essential nutritional value of milk.

* Public Health Impact: Pasteurization has been a cornerstone of public health for over a century, significantly reducing the incidence of milkborne diseases. Keywords: foodborne illness, milkborne diseases, E. coli, Salmonella, Listeria.

Practical Tips & Consumer Recommendations

Here are some actionable steps you can take to ensure your safety:

* Choose Pasteurized Dairy: Always opt for pasteurized milk and dairy products. Check the label to confirm.

* Avoid Raw Milk: Do not consume raw milk or products made from raw milk.

* Safe Handling Practices: Practice good hygiene when handling milk and dairy products, including washing your hands thoroughly.

* Stay Informed: Monitor updates from the CDC and FDA regarding the H5N1 situation.

* Report Illness: If you develop flu-like symptoms after potential exposure to dairy cattle, consult a healthcare professional. Keywords: safe food handling, flu symptoms, public health alerts.

Real-World Example: Pasteurization’s Past