H5N1 bird flu can survive in raw milk cheese for up to 120 days, raising safety concerns.

A new study finds the H5N1 bird flu virus can survive in raw milk cheese for up to 120 days, even after aging beyond the FDA’s 60-day minimum, particularly in cheeses with a pH of 5.8 to 6.6 like cheddar, but not in highly acidic cheeses like feta. Researchers detected infectious virus in both lab-made and commercial cheddar samples, though ferret tests showed no infection from cheese, suggesting raw milk may pose a higher transmission risk. The findings, led by Cornell University and funded by the FDA and New York State, urge testing milk before cheese production or using sub-pasteurization to reduce risk while preserving raw milk cheese characteristics.