Preliminary results of tests on an Ebola vaccine to be published later Friday in British science magazine The Lancet have shown "promising" results, World Health Organization Director-General Margaret Chan said.

"Early results of the vaccine are exciting and promising," Chan said, adding: "If they are confirmed it will change the management of the Ebola outbreak."

More than 11,200 people have died in an Ebola outbreak in west Africa that began in late 2013 in Guinea -- the worst on record.