Completing Ebola vaccine trials "a challenge" as epidemic wanes

GENEVA, April 10 (Reuters) - Falling Ebola cases in West Africa make completing big clinical trials on experimental vaccines a challenge, with the best hope resting on a study in Guinea, the World Health Organization said on Friday.

While the waning epidemic is good news for long-suffering populations in the region, it makes it harder for healthcare experts and drug companies to see if vaccines can protect people against the deadly fever.

There were only 30 confirmed cases of Ebola reported in West Africa in the past week, the smallest number in nearly a year in the worst ever outbreak of the viral infection.

"The issue is - can we complete a Phase III trial in humans?" Bruce Aylward, who is leading the United Nations health agency's response to Ebola, told reporters. "That will be a challenge."

Ebola is receding in Liberia, which reported no cases in the week to April 5, and in Sierra Leone, which reported nine. But it is still spreading in western Guinea, including the capital Conakry.

Last month, Guinea started testing an experimental Ebola vaccine from Merck (LSE: 0O14.L - news) and NewLink Genetics (Berlin: 4NX.BE - news) on affected communities in Ebola hotspots. The plan is to immunise the high-risk contacts around Ebola patients, thereby creating a "ring of immunity".

So far, subjects have been vaccinated in seven such rings, with the target being 100, and Aylward said the Guinea study was "the most likely to generate a meaningful answer".

Even (Taiwan OTC: 6436.TWO - news) if large clinical trials in West Africa fail to produce definitive answers on efficacy, vaccines could still be submitted to regulators using efficacy data from non-human primate experiments, plus proof of safety and immune system response in humans.

Other Ebola vaccines are also being developed by GlaxoSmithKline (Other OTC: GLAXF - news) and Johnson & Johnson (NYSE: JNJ - news) , working with Bavarian Nordic (LSE: 0DPB.L - news) .

The WHO believes West Africa's Ebola epidemic still poses a threat to other countries, but the risk of it spreading internationally appears to be diminishing.

(Reporting by Stephanie Nebehay; Writing by Ben Hirschler; Editing by Tom Heneghan)