Public health officials have just reported the first known “severe” case of bird flu in the United States. There are now 61 confirmed cases across eight states. This week, the Centers for Disease Control and Prevention (CDC) announced that a person had been hospitalized with a “severe case” of bird flu.

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.

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.