The World Health Organization will start large-scale testing of an experimental Ebola vaccine in Guinea on Saturday to see how effective it might be in preventing future outbreaks of the deadly virus. 

The West African nations of Sierra Leone, Liberia and Guinea have been hardest hit in the yearlong Ebola outbreak, which has left more than 9,800 people dead. In a statement Thursday, the U.N. health agency said the vaccine study will focus on Basse Guinee, the region that has Guinea's most Ebola cases.

The health agency's vaccination strategy in Guinea aims to create a buffer zone around an Ebola case to prevent its further spread - an approach used to eradicate smallpox in the 1970s. Officials will vaccinate people who have already been exposed to Ebola cases and are at risk of developing the disease.

The vaccine being tested - VSV-EBOV - was developed by Canada and is now licensed to Merck. A second vaccine - one developed by U.S. National Institutes of Health and GlaxoSmithKline - will be tested in a separate study as supplies become available. The Guinea trial is being conducted with other health partners including Doctors Without Borders, Epicentre, the Norwegian Institute of Public Health and the Guinean government.

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

Bertrand Draguez, medical director of Doctors Without Borders, applauded the move, which he called long overdue.

"For more than a year, we have been racing around the clock to stop the epidemic from spreading further," he noted.

On Wednesday, WHO reported 132 new Ebola cases last week, an increase from the 99 cases reported the previous week. The agency said the spread of Ebola remains "widespread" in Sierra Leone and noted that cases have jumped both there and in Guinea.

WHO said only about half of new Ebola patients in Guinea are connected to known cases, meaning that health officials are unable to track where the disease is spreading in the other half of cases. WHO also said unsafe traditional burials - a high-risk factor for Ebola transmission - continue to occur in both Guinea and Sierra Leone.

Officials also said the number of Ebola deaths taking place outside of hospitals still remains high in Guinea and Sierra Leone, "suggesting that the need for early isolation and treatment is not yet understood, accepted or acted upon."

WHO had previously set a goal of isolating all Ebola cases and ensuring all burials were safe by January 1. Authorities in Liberia planned to discharge the country's last Ebola patient on Thursday. It will take 42 days of no new cases for Liberia to be declared Ebola-free by WHO standards.