Scientists at Oxford University have launched the first clinical tests of a new Ebola vaccine approach, using a booster developed by Denmark's Bavarian Nordic that may improve the effects of a shot from GlaxoSmithKline.

Thirty healthy volunteers in Britain who have already received the experimental Ebola vaccine being developed by GSK and the U.S. National Institutes of Health will get the booster shot, researchers said on Thursday.

Adrian Hill, who is leading the trial at Oxford University’s Jenner Institute, said it was important to explore all avenues.

"If a single dose of an Ebola vaccine is sufficient, it makes absolute sense to use that. But it also makes sense at this early stage of trials to see if a second booster vaccine can greatly increase the levels of immune responses produced," he said.

As neither vaccine contains infectious material, they cannot cause a person who is vaccinated to become infected with Ebola.

Drug companies and scientists are racing to develop an effective vaccine to help fight the world's worst Ebola outbreak, which has killed some 6,000 people in West Africa, and they are collaborating to try and find the best approach.

Johnson & Johnson is also working with Bavarian to develop another so-called prime-boost vaccine and a spokeswoman for the U.S. group said trials with its product were expected to start "very soon".

Prime-boost involves a first vaccination to stimulate an initial immune response and a second shot a few weeks later to boost that response further.

Another experimental Ebola vaccine is also being developed by Merck & Co and NewLink.

Some Ebola experts say it is unlikely the epidemic can be brought under control without the use of a vaccine, which if successful could protect healthy people from being infected with the contagious and deadly virus.