The World Health Organisation (WHO) has allocated 20,000 doses of the Ervebo Ebola vaccine for a major clinical research programme in the Democratic Republic of Congo (DRC). This move aims to contain the expanding outbreak of the deadly Bundibugyo virus. The research programme, taking place in Ituri Province, will enroll frontline health workers and other personnel involved in the response. The goal is to determine whether Ervebo can protect against the Bundibugyo strain.
The outbreak in the DRC has recorded 7,733 confirmed cases and 3,732 deaths as of September 20, according to WHO data. The virus has spread across 63 health zones and seven provinces. Ituri Province remains the epicenter of the outbreak, although the proportion of total cases originating from the province has gradually declined as the virus has established transmission elsewhere. The expansion raises concern over further transmission towards international borders.
Ervebo has previously demonstrated high effectiveness against the Zaire Ebola virus but its effectiveness against Bundibugyo remains unknown. WHO advisers recommend that its use against the current strain should initially be restricted to research protocols rather than routine outbreak vaccination. This is due to the uncertainty surrounding Ervebo's effectiveness against Bundibugyo. The International Coordinating Group on Vaccine Provision initially released 70,000 doses of Ervebo to the DRC.
Of the 70,000 doses allocated, 20,000 doses were designated for the Phase 3 clinical trial, while 50,000 were intended for frontline and healthcare workers under current WHO recommendations. The trial represents both an immediate effort to protect people at high risk of exposure and an attempt to generate scientific evidence that could shape the response to future Bundibugyo outbreaks. There is currently no licensed vaccine specifically approved for Bundibugyo virus disease.
The outbreak is unfolding amid insecurity, displacement, and a wider humanitarian crisis in eastern DRC, complicating surveillance, contact tracing, access to affected communities, and delivery of healthcare. WHO continues to strengthen response operations, community engagement, and cross-border preparedness. The agency has described the 2026 Bundibugyo outbreak as the largest Ebola outbreak ever reported in the DRC.
WHO's updated emergency guidance says evidence from laboratory, animal, and observational studies indicates that Ervebo could potentially provide some cross-protection against Bundibugyo virus. However, the evidence remains insufficient to establish clinically meaningful protection in humans. For this reason, WHO's Strategic Advisory Group of Experts on Immunisation (SAGE) has recommended that Ervebo should initially be used against Bundibugyo only within research protocols.
The central scientific question surrounding the vaccination programme is whether Ervebo can protect against Bundibugyo virus. WHO has stressed that the uncertainty surrounding Ervebo's effectiveness against Bundibugyo must be clearly communicated to those receiving the vaccine. The agency also says vaccination cannot replace other proven outbreak-control measures. The research programme aims to generate scientific evidence that could inform future responses to Bundibugyo outbreaks.
Key points
- WHO allocates 20,000 Ervebo doses for clinical research in DRC to combat expanding Bundibugyo outbreak.
- Ervebo's effectiveness against Bundibugyo remains unknown, prompting WHO to restrict its use to research protocols.
- The DRC outbreak has recorded 7,733 confirmed cases and 3,732 deaths as of September 20.
