News this spring that at least three U.S. dairy farm workers got mildly ill from a bird flu virus, transmitted to cows by infected chickens, stirs concern about a possible new pandemic. That's not a danger, doctors say. No person-to-person bird flu transmission is reported, and federal agencies are watching for any wider spread of the virus among people.

Avian flu is widespread among wild birds in America and globally. It originally was identified in geese in China in 1996 and in Hong Kong residents the next year. In 2024, the federal Centers for Disease Control (CDC) recorded poultry outbreaks in 48 states as of last month. The recent spread to milk cows was confirmed in Texas and Kansas in March. Since then, more than 80 dairy herds in nine states have tested positive for the virus. Some infected cows died. Others were slaughtered if they didn't recover and test negative.

The flu also jumped to a few farmworkers. Symptoms range from mild (runny eyes, cough) to severe illness such as pneumonia, which earlier caused deaths in other countries. Nearly 900 people around the world caught avian flu in the two decades between 2003 and 2024. (This spring's U.S. victims all recovered after receiving medication.)

Dairy cows are a "new and unexpected host" of the virus, according to the CDC, where specialists worry that it could mutate (change) in them -- making it easier to spread to pigs, other animals or potentially humans. But there's no safety fears about dairy items from stores because only milk from healthy animals can be sent into processing – called pasteurizing – that kills bacteria and viruses. "People should not prepare or eat uncooked or undercooked food or related uncooked food products, such as unpasteurized (raw) milk,” the CDC advises.

Doctor says: "In the short term, there is very little threat. In the coming years or decades, however, I'm much more concerned. It's natural to wonder if it's only a matter of time before this virus is able to spread among humans." – Dr. Scott Roberts, Yale School of Medicine infectious diseases specialist

Affected states: Herds were infected in Colorado, Idaho, Kansas, Michigan, New Mexico, North Carolina, Ohio, South Dakota and Texas, as of May.

Any vaccine? Seasonal flu shots don't prevent bird flu infection, and no other vaccines protect against getting it. Preliminary work toward a targeted vaccine is under way in case it's needed, the CDC says.