U.S. health officials are telling Americans to take precautions if they travel to Uganda because of an Ebola outbreak.

Uganda has launched a trial of a vaccine against the Sudan strain of the Ebola virus, following an outbreak in the country with three confirmed cases.The first patient, a 32-year-old male nurse, died last week.

Test results on the sick people are pending, and a top WHO official said the outbreak response is proceeding rapidly.