An experimental Ebola vaccine developed in the U.S. appears to be safe and promising in an early clinical trial, according to new findings.

The vaccine made by British pharmaceutical giant GlaxoSmithKline and the U.S. National Institutes of Health (NIH) is being developed to combat the Sudan and Zaire strains of the Ebola virus, the latter the one behind the current deadly outbreak in West Africa.​

The trials were conducted at the NIH in Bethesda, Md., with 20 healthy participants who received doses of the vaccine.

The participants developed antibodies to Ebola, researchers said in Wednesday's New England Journal of Medicine. But the researchers note participants' immune responses depended on the dose and were also associated with minor side-effects.

Clinical trials of the vaccine are continuing. The NIH is in talks with Liberian officials about doing the next tests in West Africa, though details have yet to be released.

The World Health Organization has said it hopes to begin testing experimental vaccines as early as January on more than 20,000 front-line health-care workers and others in West Africa's hot zone.

"Perhaps one of the only silver linings of the [Ebola] crisis that has shaken West Africa over the past year is that the event has pushed therapeutics and vaccines for [Ebola], which had previously been relatively stalled in development despite the promising results in nonhuman primates, into accelerated production and clinical trials," Dr. Daniel Bausch, who is not one of the vaccine's researchers, wrote in an editorial published alongside the trial findings.

Meanwhile, a Canadian-developed Ebola vaccine is also currently undergoing human clinical trials in Canada and the U.S., with additional tests to be done in Germany, Switzerland, Gabon and Kenya.

WHO reported on Wednesday that there have been 5,689 Ebola deaths out of nearly 16,000 cases. Almost all cases and all but 15 deaths have been in Guinea, Sierra Leone and Liberia — the three hardest-hit countries, which reported 600 new cases in the past week.