When, where and how the H5N1 bird flu virus may evolve and its capacity to spark a pandemic is hard to predict — in part, some researchers say, because of federal restrictions on gain-of-function research.

Mississippi has confirmed H5N1 in a poultry flock. The birds are not part of food supply chain. What you need to know about bird flu symptoms, risk.

The United States has confirmed its first known severe human infection of H5N1 bird flu, in a person in Louisiana believed to have contracted the virus through contact with sick or dead birds in a backyard flock.