The experimental Ebola vaccine, developed by Merck and NewLink Genetics, will enter Phase III of testing in Guinea on March 7, weeks after a similar test began in neighboring Liberia, the World Health Organization (WHO) said on Thursday.

The VSV-EBOV vaccine is one of two currently under development. The other, CAd3 from Britain's GlaxoSmithKline, is also already undergoing the test in Liberia.

"If a vaccine is found effective, it will be the first preventive tool against Ebola in history," WHO chief Margaret Chan said in a statement.

The two vaccines have both passed safety tests on humans.

The tests on VSV-EBOV will take place in areas of Basse Guinee, the region with the highest number of current cases in Guinea.

Up to now, there has been no licensed treatment or vaccine for the Ebola virus, which has killed some 9,800 people since the present outbreak began in December 2013.

The overwhelming majority of deaths have occurred in Guinea, Liberia and Sierra Leone.

Ebola-free week for Liberia

In a sign that the disease is receding, the WHO said on Wednesday that Liberia, the worst-hit country in terms of fatalities with 4,117 deaths, had gone a full week without reporting any new confirmed Ebola cases for the first time since May.

Health authorities in the country have also said that they were preparing to discharge the last Ebola patient in the West African country.

The head of the Incidence Management System, Tolbert Nyenswah, on Wednesday confirmed the planned release, saying that with no other confirmed cases of Ebola in the country, Liberia could begin to count the 42 days necessary to be declared Ebola-free according to official WHO standards.

Guinea and Sierra Leone, however, did not have the same kind of positive news, with significant increases in new confirmed cases in both countries.

Sierra Leone registered 81 new cases, an increase of 16 over the week before, while Guinea reported 51 cases, also 16 up.

The WHO has warned that the number of new cases suggested that "the need for early isolation and treatment is not yet understood, accepted or acted upon."

The Ebola virus, which causes often fatal hemorrhaging, organ failure and severe diarrhea, is passed on by contact with bodily fluids, meaning that health workers looking after Ebola patients are particularly at risk.

Nearly 500 health workers have died so far in the epidemic.

tj/kms (AFP, Reuters)