The U.S. Centers for Disease Control and Prevention on Thursday warned doctors and other healthcare workers about an outbreak of Ebola cases in Uganda.

Ugandan authorities have begun a clinical trial of a vaccine against the Sudan strain of Ebola that has killed one person in the outbreak declared last week.

U.S. health officials on Wednesday urged Americans traveling to Uganda to take precautions because of an Ebola outbreak — and said they are helping Ugandan health officials respond to the threat. The Centers for Disease Control and Prevention travel alert does not call on travelers to steer clear of Uganda,