With reports of the first human death from bird flu in the US, some Americans are feeling an uncomfortable flashback to the early days of Covid-19, when infectious disease experts were talking about a new virus that was sending people to the hospital with respiratory infections.

A variant of the virus caused disease in people in 1997, when there was a small but deadly outbreak in Hong Kong. Eighteen people had confirmed diagnoses, and six of them died. Since then, there have been sporadic cases around the world—but no large outbreaks.

Louisiana has reported the first U.S. fatality from avian influenza. Most of the country’s human cases have been mild

In its announcement this week of the first human death from bird flu in the United States, health officials in Louisiana were quick to note that the patient was over age 65 and “reported to have underlying medical conditions.

Any time a person catches H5N1, or bird flu, their infection is a chance for the virus to mutate in the wrong direction. When someone dies from the bird flu—as an elderly Louisiana man did on Jan. 6,

Moderna surged as investors turned eyed potential demand for a vaccine to protect against bird flu after the US reported its first death from the virus.