STRIVE trial
2015 Sierra Leone trial of the rVSV-ZEBOV Ebola vaccine in health and frontline workers.
STRIVE, the 2015 Sierra Leone vaccine trial, ended as a safety study because cases fell too fast; in 2026 WHO expects a Bundibugyo ring trial to start in DR Congo in October or November, after Ituri's cases passed a mid-August peak.
Last refreshed: 4 October 2026
Timeline for STRIVE trial
Mentioned in: WHO: 2,000 Congolese workers get Ervebo
Pandemics and BiosecurityBackground
STRIVE, the Sierra Leone Trial to Introduce a Vaccine Against Ebola, tested the rVSV-ZEBOV vaccine now sold as Ervebo. It began in April 2015, run by the US CDC with Sierra Leone's College of Medicine and Allied Health Sciences and the country's health ministry.
The trial enrolled more than 8,650 health and frontline workers in five districts and vaccinated about 8,000 of them, comparing immediate with deferred vaccination. It found no vaccine-related serious adverse events. West Africa's epidemic was waning by then, and cases fell too fast to measure efficacy, so STRIVE ended as a safety study.
Guinea's ring trial of the same vaccine, begun in April 2015, showed that the vaccine protected, because that trial still had steady clusters of new cases. WHO's 2026 ring trial is planned for Ituri, where cases have fallen since a mid-August peak.
STRIVE ended as a safety study
STRIVE could not measure efficacy in 2015 because Sierra Leone's cases fell too fast. In 2026 WHO planned a Phase 3 ring-vaccination trial of 20,000 Ervebo doses against Bundibugyo ebolavirus, to begin in Ituri in October or November. Ituri's cases have fallen since a mid-August peak; in 2015 falling cases turned STRIVE into a safety study.
STRIVE vaccinated about 8,000 health and frontline workers in 2015, and the 2026 response also starts with workers. About 2,000 Congolese frontline workers had received Ervebo by 10 September from 70,000 doses released on 20 August, and BRAVO, MSF's Ervebo study for some 20,000 frontline staff across Ituri and North Kivu, opened in Bunia on 19 September. In early October 2026 the ring trial was still planned, not under way.