WHO recommends clinical trial of Ebola vaccine against Bundibugyo virus

The World Health Organization (WHO) has recommended prioritizing a randomized clinical trial for the Ervebo vaccine against Bundibugyo virus disease in the Democratic Republic of Congo (DRC). This recommendation stems from preliminary animal study data indicating the vaccine might provide some cross-protection, notably in lowering mortality rates.

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The recommendation followed preliminary animal study data suggesting that the vaccine may provide some cross-protection against the disease, particularly in reducing deaths.

The recommendation was made by WHO's Technical Advisory Group on Candidate Vaccine Prioritisation on July 31, following a review of the vaccine's safety, efficacy, availability, and feasibility. The DRC is currently responding to an outbreak of Ebola disease caused by the Bundibugyo virus, declared on May 15, 2026. As of July 30, the WHO reported 3,605 confirmed cases and 1,587 deaths from this outbreak.

Ervebo was originally developed to combat Ebola virus disease caused by the Zaire virus, not the Bundibugyo virus. Initially, the advisory group cautioned against using Ervebo outside controlled research settings due to uncertainty about its effectiveness against the Bundibugyo virus. However, new preliminary animal data showing potential cross-protection, especially in reducing deaths, prompted the revised recommendation for clinical trials.

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The advisory group found no identified safety concerns with the use of Ervebo among contacts of confirmed cases during a Bundibugyo virus disease outbreak.

The Bundibugyo virus causes a severe form of Ebola disease, distinct from the Zaire strain. The current outbreak in the DRC is the first of its kind in the country. WHO notes that there is no licensed vaccine or specific treatment for Bundibugyo virus disease, which has historically recorded case fatality rates between 30% and 50%. While the advisory group found no immediate safety concerns with Ervebo's use among contacts of confirmed cases during the outbreak, they stressed that its effectiveness in preventing transmission remains unproven and requires evaluation through clinical research. The WHO stated that a vaccine specifically targeting the Bundibugyo virus would be the preferred option, though data on such candidates are not yet available.

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However, the experts stressed that the vaccine’s effectiveness against Bundibugyo virus disease and its ability to prevent transmission have not been established.