Why Have U.S. Bird Flu Cases Been So Mild?

Since the start of the bird flu outbreak in U.S. cattle more than eight months ago, health authorities have reported 57 human cases of H5N1 viral infections, all of which have been mild. Scott Hensley, PhD, a professor of Microbiology, says that this virus isn’t inherently less severe than other flu strains, and that one or two mutations can greatly change the way this virus affects humans.