A pasteurization approach widely used in the dairy industry proved to be effective at killing bird flu in milk after all, the Food and Drug Administration announced Friday, after an earlier federal lab study raised questions about the approach. 

The FDA says its new results are the latest to show that drinking pasteurized grocery store milk remains safe, despite an outbreak of highly pathogenic avian influenza, or HPAI H5N1, on dairy farms across at least eight states. 

“We had a lot of anecdotal evidence. But we wanted to have direct evidence about HPAI and bovine milk. So we began to build this custom instrument that replicates, on a pilot scale, commercial processing,” Prater said.

It comes weeks after researchers at the National Institutes of Health found some infectious bird flu virus was able to survive pasteurization in lab tests.

Both the FDA and the earlier NIH researchers looked at an approach called “flash pasteurization” or high temperature short time processing, which heats milk for at least 15 seconds at 161°F. 

Unlike the NIH study, Prater said the study with the U.S. Department of Agriculture took longer to complete because it was designed to more accurately simulate all the steps that go into processing milk in the commercial dairy industry. 

The FDA said the tests show the pasteurization process was killing the virus even before it reached the final stages when milk is held at the right temperature, offering a “large margin of safety.”

“What we found in this study actually is that the virus is completely inactivated even before it gets into the holding tube,” Prater said. 

Virus in raw milk

Virus is likely being spread from infected cows to other animals and to humans that have worked on dairy farms through droplets of raw milk teeming with the virus, the USDA has said.

Eric Deeble, acting senior adviser for USDA’s H5N1 response, told reporters on Tuesday that none of the confirmed infected herds so far had been supplying raw milk. 

Hundreds of pasteurized milk and other dairy product samples tested by the FDA so far from grocery stores have also so far not found any infectious virus, but fragments of dead virus have turned up — suggesting missed infections.

Prater said a second round of testing is underway, which will also look at cheese made from raw milk.