While health authorities have advised against drinking raw milk because it can harbor the bird flu virus and other pathogens, health risks from cheeses made with raw milk were unclear.

A preprint study by researchers at Cornell University found that the bird flu virus can remain active in raw milk cheeses for months, raising concerns about public health risks.

In the United States, cheese made from raw, unpasteurized milk must age for 60 days before hitting store shelves. The aging process was thought to reduce pathogens, but the new study showed that it may not be long enough to kill the H5N1 bird flu virus.

No one in the U.S. has contracted bird flu from eating raw cheese, but public health experts are closely monitoring the outbreak.

“The great news is that there have been no raw milk cheeses available in the marketplace to date that have been found to have infectious virus,” Nicole Martin, PhD, co-author of the study and an assistant research professor in dairy foods microbiology at Cornell University, told Verywell in an email.

The best way to reduce bird flu risk is to avoid contact with sick birds or infected animals and refrain from consuming raw milk or raw milk products, especially from infected cows, according to the Centers for Disease Control and Prevention (CDC).

Is Raw Cheese Safe for Consumption?

The vast majority of raw milk cheese should be safe after the 60-day aging window, according to Keith Poulsen, DVM, PhD, a clinical associate professor of medical sciences at the University of Wisconsin-Madison School of Veterinary Medicine.

Research has shown that the 60-day aging period is enough time to inactivate bacterial pathogens in the cheese. Like raw milk, unaged raw cheese can carry pathogens, while aged raw cheese is generally considered safer.

“We have a lot of history and data to back that up,” Poulsen told Verywell in an email. “Unfortunately, the data from Cornell suggests that if raw milk cheeses were made on an affected farm, they would not be recommended for consumption.”

Researchers are unsure why the bird flu virus survived the aging process, but the fat and protein content in the cheese, along with the relatively low aging temperature, likely contribute to the stability of the virus, according to Martin.

Other viruses affecting cows—not humans—may also survive this aging process, but they just haven’t been studied because they don’t have the potential to cause widespread human disease, said David J. Topham MS, PhD, a professor of microbiology and immunology and founding Director of the University of Rochester Translational Immunology and Infectious Disease Institute.

“I don’t think there’s anything special about the H5N1 virus that gave it the ability to survive during the 60-day development process,” Topham said.

Should You Avoid Raw Cheese for Now?

You may not have to avoid raw cheese because of this new study.

“Most aged raw milk cheese producers are niche artisanal cheese makers, and they are likely at a lower risk for influenza infection because typically, these are closed herds, seasonal grazers, and do not move their animals in high-risk interstate transport,” Poulsen said.

If you prefer to avoid raw milk cheese as a precaution, check the ingredient list for “unpasteurized milk.” However, the Food and Drug Administration (FDA) does not require producers to disclose whether the cheese was made with unpasteurized milk. You can try contacting the producers directly if you have questions.

“Everybody needs to make their own decisions about how important it is to them to have these things, or maybe take a break, or adopt a wait-and-see attitude,” Topham said. “It’s entirely up to the individual.”

While scientists still don’t know for sure, Topham added, you would likely need to eat a large amount of contaminated cheese to be at risk.