An Ebola vaccine provided 100-percent protection in a field trial in hard-hit Guinea, researchers and officials said Friday, mooting "the beginning of the end" of the killer West African outbreak.

The world is "on the verge of an effective Ebola vaccine," the World Health Organization (WHO) said, hailing the results from the first efficacy test of the VSV-ZEBOV vaccine among people living in a high-danger zone.

"This is an extremely promising development," added WHO chief Margaret Chan.

"An effective vaccine will be another very important tool for both current and future Ebola outbreaks."

About 28,000 people have been infected in Guinea, Sierra Leone and Liberia in the worst Ebola outbreak in history, according to the WHO, and more than 11,000 have died.

VSV-ZEBOV may become the first licensed vaccine against the disease for which there is also no approved treatment or cure.

The trial showed that the vaccine "offers 100 percent protection against Ebola after roughly one week," said researcher Sven Trelle from the University of Bern.

The test, backed by drug firm Merck, the WHO and the governments of Canada, Norway and Guinea, saw 4,123 high-risk people vaccinated immediately after someone close to them fell ill with the deadly haemorrhagic fever.

None of the vaccinated group caught the virus, according to study results published in The Lancet medical journal.

A second, comparison group of 3,528 people received the vaccine only three weeks after potential exposure. Sixteen of them contracted the virus, said the study, but by day six after immunisation, the remainder of this group was also fully protected.

"Indeed, no vaccinee developed symptoms more than six days after vaccination, irrespective of whether vaccination was immediate or delayed," said the study paper.

"The initial results of the study show that the vaccine can effectively contain the further spread of the Ebola virus," added a statement from the University of Bern, which contributed to the research.

Disease experts welcomed the results.

This is big news -- the most promising medical development so far in the ongoing race to shut down Ebola," Benjamin Neuman, a virologist with the University of Reading, told AFP.

Added Peter Smith of the London School of Hygiene and Tropical Medicine, the results were "very exciting and suggest that the Ebola vaccine tested may be highly effective in protecting against Ebola disease among those in the immediate vicinity of an Ebola case."