The randomized Ebola vaccine trial – which is ongoing – began on March 23 this year in Guinea among people who had close contact with Ebola patients. It was conducted by a range of groups including the Guinean health authorities, the World Health Organization, Doctors Without Borders, and the Norwegian Institute of Public Health.
Preliminary results from the trial are due to be published today in The Lancet.
The WHO said in a press release that the vaccine, known as VSV-EBOV, has so far demonstrated "100% efficacy in individuals", although further research is needed to determine whether it will be effective at conferring the herd immunity that keeps whole populations safe from infections, even among those who are not vaccinated.
Dr Margaret Chan, director-general of the WHO, said in a statement, "This is an extremely promising development [...] An effective vaccine will be another very important tool for both current and future Ebola outbreaks."
VSV-EBOV was originally developed by the Public Health Agency of Canada and is manufactured by Merck. The trial did not involve a placebo, but was randomized by a "ring vaccination protocol", which varies the date at which volunteers get vaccinated. That randomization has now also been stopped, to ensure that all volunteers get vaccinated as early as possible.
The trial will nonetheless continue in order to gather the extra data that will be needed for the vaccine to be licensed.
Dr. Sakoba Keita, Guinea's Ebola response national coordinator, said in the WHO statement, "This is Guinea's gift to West Africa and the world. The thousands of volunteers from Conakry and other areas of Lower Guinea, but also the many Guinean doctors, data managers and community mobilisers have contributed to finding a line of defence against a terrible disease."