Forbes When a highly pathogenic avian influenza virus jumped into American dairy cows in the spring of 2024, scientists worried about the next step: spillover into humans. Sure enough, that is precisely what happened. Between March 2024 and May 2025, seventy human H5N1 infections were confirmed in the United States.
Now, a new study in Nature Medicine, led by Melissa Rolfes and colleagues at the Centers for Disease Control and Prevention (CDC), provides the first systematic look at those cases. Of the seventy infections, four required hospitalization and one proved fatal – a stark contrast to the nearly 50% global death rate for H5N1, yet still a fatality rate over a thousand times greater than that of seasonal influenza, according to CDC data.
Despite a recent lull, human infections have been almost continuous in workers exposed to infected animals. Furthermore, a small number of severe cases linked to backyard poultry suggest the risk to the general population is not insignificant.