Human H5N1 cases in the U.S. are rising. That's bad timing with flu season, bird migrations just months away

The sheer scale of the U.S. bird flu outbreak is hard to fathom. 

More than 100 million farmed birds have been infected with H5N1 since 2022, followed by roughly 170 herds of dairy cows, along with virus detections in more than 200 other mammals — humans included.

Colorado is now facing the country's first human outbreak, which has quickly hit the double-digits. As of Wednesday, there have been nine recent cases at two poultry farms, plus one earlier case from a dairy farm. And while the latest spread may be chicken-to-human, genetic sequencing suggests the virus strain is similar to the form of bird flu tearing through cow populations across more than a dozen states.