How are H5N9 and H5N1 different? What to know after California bird flu outbreak
The California duck farm's strain of H5N9 is different from those earlier cases because this time it is closely related to a newer variant of the H5N1 virus. That variant is called H5N1 D1.1, the USDA spokesperson said, which has emerged over the past year to dominate U.S. cases in wild birds and poultry.