The second-largest Ebola outbreak in history has spread to a major city in eastern Congo.
Health experts worry whether the stock of an experimental vaccine will stand up to the demands of an epidemic with no end in sight.
Butembo, with more than one million residents, is now reporting cases of the deadly hemorrhagic fever.
This complicates Ebola containment work already challenged by rebel attacks elsewhere that have made
tracking the virus almost impossible in some isolated villages.
The outbreak declared in August is now second only to the devastating West Africa outbreak that killed more than 11,300 people a few years ago.
Congo's Health Ministry said, there are currently 471 Ebola cases, of which 423 are confirmed, including 225 confirmed deaths.
The Ebola virus is spread via bodily fluids of those infected, including the dead.