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.

Shares of vaccine makers including Moderna, Novavax and CureVac rose Tuesday after U.S. health officials confirmed the first American death caused by the H5N1 bird flu. Moderna and Novavax shares rose more than 10%,

The company is one of a few drugmakers currently developing a vaccine for the illness, which is spreading rapidly through North America.

Moderna stock was on track to see a weekly gain of 10% as of Wednesday following the first reported bird flu death in the US.

The U.S. will rebuild its stockpile of bird flu vaccines for poultry matched to the current strain of the virus circulating among commercial flocks and wild birds, the Department of Agriculture said on Wednesday.

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,

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.