The University of Oxford began human trials of its Ebola vaccine, raising hopes that the spread of the Bundibugyo strain may be halted before it becomes the biggest-ever outbreak.
The virus has spread across much of the Democratic Republic of Congo, with officials there saying it had reached two new provinces.
The US said it would block American citizens in the DRC from traveling back home until they have spent 21 days in a third country, leaving dozens stranded.
The spread of the disease, which has led to more than 700 deaths in the DRC and parts of Uganda, has been aided by rampant misinformation and a major deficit in health supplies.