Britain's Wellcome Trust said that clinical trials it was funding for a new Ebola vaccine in Liberia were halted today due to a fall in new cases.
"The current position is that there is no realistic prospect of the trial enrolling sufficient patients to be able to reach a conclusion about the efficacy of the drug," the Wellcome Trust, Britain's biggest scientific research charity, said in a statement.
"Therefore the trial has been terminated," it added.
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The Wellcome Trust said the decision was taken on Tuesday after the pharmaceutical company Chimerix, which manufactures the brincidofovir vaccine, said it was withdrawing from the trial on Friday.
The first large-scale trials of two other Ebola vaccines -- GlaxoSmithKline's Chad3-EBO-Z and rVSV-ZEBOV, manufactured by Merck and Newlink began in Liberia yesterday.
Today's decision was taken by the Trial Steering Committee, which includes scientists from Liberia, the University of Oxford and Medecins Sans Frontieres.
"We're delighted that infections are falling, but fewer patients makes it more difficult to carry out the robust scientific studies needed," Peter Horby from the University of Oxford, who was leading the trial, said in a statement.
Jeremy Farrar, director of the Wellcome Trust, which is funding a multi-million pound therapeutics platform for experimental Ebola treatments, said it was "disappointing" that the trial could not continue.
"It is essential that other studies of potential treatments and vaccines continue and hopefully will still be able to deliver meaningful results for this and the inevitable future epidemics of Ebola," he said.
Stephen Kennedy, a study investigator from the Pacific Institute for Research and Evaluation in Liberia added: "The scientific community will move on without any clear evidence regarding the role of brincidofovir in the management of Ebola."
Weekly Ebola infections in west Africa have dropped to below 100 for the first time in more than six months, the WHO said last week, raising hopes the worst-ever outbreak of the virus is coming to an end.
The World Health Organisation said it had now shifted its efforts in Guinea, Liberia and Sierra Leone, the countries worst-hit by the epidemic from slowing the spread to stamping it out completely.
