Health experts say it has not been possible to begin a trial in Uganda of three experimental Ebola vaccines due to a lack of cases of the virus.
An outbreak of the Sudan strain of Ebola has caused at least 55 deaths since September.
But there have been no new cases since late last month, and the World Health Organization has praised efforts to contain the outbreak.
It says if no further cases are reported in the next few weeks, it will have to look at other ways to test the safety and effectiveness of the vaccines.
Uganda has received more than 5,000 doses and was planning to vaccinate close contacts of those infected.
