A prototype vaccine for Ebola may be "up to 100 percent effective" in protecting against the deadly virus, the World Health Organization (WHO) said Friday.
If all goes well, the vaccine could become available in 2018 under a fast-track approval process, it said.
In a major clinical trial, nearly 6,000 people in Guinea were given the test vaccine last year, at the tail end of a lethal epidemic of Ebola.
Not one of the 6,000 contracted the disease.
But in a control group of volunteers that did not receive the vaccine, 23 Ebola cases occurred, researchers reported in The Lancet medical journal.
"If we compare zero to 23, this strongly suggests that the vaccine is very effective, that it could be up to 100 percent effective," Marie-Paule Kieny, WHO's assistant director-general and lead author of the study said
Her team of three dozen researchers calculated a 90-percent likelihood during a full-fledged epidemic that the vaccine, dubbed rVSV-ZEBOV, would work in more than 80 percent of cases.
"After 40 years, we appear to now have an effective vaccine for Ebola virus disease to build upon," Thomas Geisbert, a scientist at Galveston National Laboratory in Texas who did not take part in the study, wrote in a commentary, also in The Lancet.