Medical experts advise that people should get a vaccine for the bird flu when it becomes commercially available. One doctor said the most at-risk patients should be first.

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.

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.