The virus has recently expanded in two ways: across regions and across species. Rather than being concentrated in Asia, bird flu has moved across much of the planet. And it has infected a wider variety of animals, including mammals. ( This Times story explains .) Dairy cows in many parts of the United States have tested positive.

H5N1 bird flu is spreading among animals and humans, raising concerns about mutation risks. While human cases are mild, experts stress urgent preparedness for potential pandemics and vaccine readiness gaps.