The Ebola outbreak that has been spreading across the Democratic Republic of the Congo and Uganda since May has now surpassed 3,200 confirmed cases and 1,400 deaths, making it the second-largest Ebola outbreak ever recorded after the 2014-2016 West Africa epidemic. It is caused not by the Zaire ebolavirus, the species that killed more than 11,000 people in West Africa and for which a highly effective vaccine exists, but by the Bundibugyo virus, a separate species of the Ebola family for which there is no licensed vaccine and no specific treatment.
The global response to Ebola outbreaks has been built around the tools developed for Zaire ebolavirus. The recombinant vesicular stomatitis virus vaccine, sold as Ervebo, was licensed in 2019 after demonstrating high efficacy during clinical trials in Guinea. It is stockpiled by the International Coordinating Group and deployed during Zaire ebolavirus outbreaks, but it does not protect against Bundibugyo virus. The monoclonal antibody therapies that have dramatically reduced mortality for Zaire infection, Inmazeb and Ebanga, were developed for and tested against that species and have not been validated for Bundibugyo.
The current outbreak, first confirmed in early May 2026 in the DRC’s Ituri province, has expanded with alarming speed. The CDC reports that the outbreak surpassed 1,000 confirmed cases within 40 days of the response being activated. By comparison, the catastrophic 2018 outbreak in North Kivu, also in the DRC, took approximately 235 days to reach the same threshold. Ituri province remains the epicenter, accounting for 2,848 of the 3,200 confirmed cases in the DRC as of July 25. Uganda has reported 20 confirmed cases, all in Kampala and all linked to travel from the DRC, with no evidence of community transmission within Uganda. A single travel-associated case has been confirmed in France, in a patient who had been in the DRC.
The case fatality rate stands at approximately 44 percent, lower than the roughly 50 to 90 percent range observed for Zaire ebolavirus in previous outbreaks but still devastating. The majority of deaths have occurred in Ituri, where insecurity, constrained access for response teams, and the displacement of populations have hampered both surveillance and clinical care. The DRC government and the World Health Organization have deployed response teams, but security-related incidents affecting health facilities have disrupted contact tracing and vaccination planning.
Vaccination planning in a Bundibugyo outbreak requires a fundamentally different approach. Since no licensed Bundibugyo vaccine exists, the WHO Technical Advisory Group on Candidate Vaccine Prioritization convened in May to evaluate which experimental candidates should be tested in the field. On July 2, the WHO added the first diagnostic test for Bundibugyo virus disease to its Emergency Use Listing, a necessary precursor to running vaccine and treatment trials that rely on accurate case identification. Patient enrollment has begun in a clinical trial designed to identify the first effective treatments specifically for Bundibugyo virus disease, operating under the WHO’s Solidarity-like framework.
Several vaccine candidates are in the pipeline. The most advanced is believed to be a candidate developed by the Sabin Vaccine Institute, which has experience with filovirus vaccines and has been working on a multivalent approach that could cover multiple Ebola species. Moving a candidate from the laboratory to field deployment during an active outbreak requires navigating regulatory approval, manufacturing scale-up, cold-chain logistics, and community acceptance, all while new cases continue to appear. The WHO has issued emergency guidance on the use of the licensed Zaire ebolavirus vaccine during Bundibugyo outbreaks, acknowledging that while it is not expected to be effective against Bundibugyo, it may still be considered for use under certain circumstances due to the absence of alternatives.
The outbreak’s trajectory depends on whether the response can accelerate faster than the virus. Bundibugyo virus was first identified in 2007 during an outbreak in the Bundibugyo district of western Uganda, where it infected 149 people and killed 37. A second outbreak in the DRC in 2012 infected 57 and killed 29. Both were relatively small and contained without the need for large-scale vaccine deployment. This is the first time Bundibugyo virus has spread at this scale, and the first time the global health system has confronted a large Ebola outbreak without the vaccines and treatments that have become the standard tools for Zaire ebolavirus.
References
World Health Organization. Ebola disease caused by Bundibugyo virus, Democratic Republic of the Congo & Uganda. Disease Outbreak News, 3 July 2026.
Centers for Disease Control and Prevention. Ebola Outbreak: Current Situation – DRC and Uganda, 2026. Data as of 25 July 2026.
World Health Organization. Patient enrolment begins in a scientific trial to identify the first effective treatments for Bundibugyo virus disease. News release, 2 July 2026.
World Health Organization. WHO adds first diagnostic test for Ebola Bundibugyo virus to its Emergency Use Listing. News release, 2 July 2026.
World Health Organization. WHO Technical Advisory Group on Candidate Vaccine Prioritization: meeting report, 19 and 25 May 2026.