Phase III trials for an Ebola vaccine are set to launch Saturday in Guinea, one of the countries most gravely affected by the Ebola outbreak that began in 2014, the World Health Organization announced Thursday. The vaccine, VSV-EBOV, was developed by the Public Health Agency of Canada and will be tested in Basse Guinée, the area of Guinea currently afflicted with the highest number of Ebola cases, according to the WHO. 

These particular trials, which are the final stages of testing for VSV-EBOV, will use what is known as “ring strategy.” In this method, similar to the one used to eradicate smallpox, anyone who is found to have come into contact with someone newly diagnosed with Ebola and who gives consent will be vaccinated. The trial will test whether the vaccine not only prevents those who are vaccinated from catching Ebola but also whether vaccinating them prevents the virus from spreading further. The vaccine will also be offered to frontline medical and health care workers in the same region.

Even as Liberia released its final Ebola patient from the hospital Thursday, the number of confirmed Ebola cases has increased in Sierra Leone and Guinea in recent weeks. Guinea had 51 new cases in the week ending March 1, and the previous week, it reported 35 new cases, according to data from the WHO. Nearly 10,000 people in those three West African countries have been killed by the virus in the ongoing outbreak.

“The Ebola epidemic shows signs of receding but we cannot let down our guard until we reach zero cases,” Marie-Paule Kieny, an assistant director-general in charge of Ebola research and development at the WHO, said in the organization’s statement. An effective vaccine would be a game-changer in the current epidemic as well as possible future ones, she said. This vaccine trial is a joint effort by the WHO, the Guinean health ministry, medical nongovernmental organization Doctors Without Borders, Epicentre and the Norwegian Institute of Public Health.