WHO moves Ebola treatments and vaccines into new trials after fresh outbreak concerns
The World Health Organization on May 28, 2026, announced it had moved candidate treatments and vaccines for Bundibugyo virus disease into clinical trials in response to an outbreak in the Democratic Republic of the Congo and Uganda. WHO officials said the decision aimed to generate robust safety and efficacy data for unlicensed Ebola products while ensuring ethical research during the emergency.
The advisory groups also supported evaluating combination therapy using a monoclonal antibody plus remdesivir to determine whether dual-agent regimens improve patient outcomes. None of these treatments is currently licensed specifically for Bundibugyo Ebola, but they were selected based on promising preclinical or prior clinical data against Ebola viruses, according to WHO.
WHO expert groups recommended prioritizing three candidate therapeutics for clinical trials among confirmed Bundibugyo virus disease (BVD) cases: the monoclonal antibodies MBP134 and Maftivimab®, as well as the antiviral remdesivir, the agency said in a May 28 statement.
WHO officials emphasized that these candidate therapies must be administered exclusively within structured clinical trials that include standardized protocols, data collection, and ethical oversight, rather than as part of routine care. Access to these investigational treatments will be limited to patients with laboratory-confirmed BVD in affected areas of the Democratic Republic of the Congo (DRC) and Uganda, the two countries currently experiencing cases, WHO said.
On the vaccine front, WHO experts identified a single-dose recombinant vesicular stomatitis virus (rVSV) Bundibugyo vaccine developed by the International AIDS Vaccine Initiative (IAVI) as the most promising candidate for prevention. According to WHO, this vaccine is expected to require approximately seven to nine months before doses are ready for clinical efficacy trials. A second candidate vaccine, ChAdOx1 Bundibugyo, developed by Oxford University in collaboration with the Serum Institute of India, could be available for efficacy assessment in about two to three months, pending additional animal data to support further prioritization, WHO officials said.
WHO cautioned that the only currently licensed Ebola vaccine, Ervebo (rVSV-ZEBOV-GP), which targets the Zaire Ebola virus species, is not approved for Bundibugyo virus disease. Evidence for cross-protection against Bundibugyo is limited and inconclusive, so WHO advised restricting its use to carefully designed research settings during the current outbreak.
For post-exposure prophylaxis (PEP) among contacts of confirmed or probable BVD cases, WHO experts prioritized the oral antiviral obeldesivir for evaluation in clinical trials. Planned research involves administering obeldesivir tablets to identified contacts and monitoring whether the treatment prevents disease development. WHO noted, however, that effective PEP implementation depends on strong contact-tracing systems, which remain operationally challenging in some affected areas of the DRC.
WHO is working closely with the governments of the DRC and Uganda to facilitate and implement clinical research evaluating the prioritized treatments and vaccines during the ongoing Bundibugyo outbreak. The agency convened multiple expert and advisory groups focusing on epidemic-prone diseases, ethics, regulatory issues, and clinical management to review evidence and recommend a research strategy, according to WHO.
The current approach builds on lessons learned from previous Ebola vaccine trials. Notably, Uganda’s Ministry of Health and WHO launched the first-ever clinical efficacy trial for a Sudan-species Ebola vaccine on February 3, 2025, in Kampala. That trial used a ring-vaccination cluster-randomized design to evaluate a single-dose rVSV candidate vaccine among contacts and contacts-of-contacts of confirmed Sudan virus disease cases. Prior Phase 1 safety and immunogenicity data supported the trial design.
WHO’s Global Advisory Committee on Vaccine Safety has reported reassuring safety profiles for licensed Ebola vaccines, including Ervebo and the Ad26.ZEBOV/MVA-BN-Filo regimen, with more than 6,500 adults and 649 children vaccinated in various studies. The rate of grade 3 fever in children within seven days post-vaccination was less than 1.5%, according to WHO records. Earlier trials such as the “Ebola ça Suffit” study demonstrated high protection with rVSV-EBOV in West Africa, establishing ring vaccination and rapid deployment as effective outbreak strategies.
The rVSV Bundibugyo vaccine candidate is under development by IAVI, an international nonprofit organization with prior experience in rVSV-based Ebola vaccines. The ChAdOx1 Bundibugyo vaccine is being developed by Oxford University in collaboration with the Serum Institute of India, leveraging adenovirus-vector platforms similar to those used in other viral vaccines. Animal studies for the ChAdOx1 candidate are already underway, with WHO describing it as a promising candidate if animal data support further advancement.
WHO noted that the new Bundibugyo trials are planned amid an ongoing outbreak in the DRC, with cross-border spread to Uganda prompting an accelerated research response. While the licensed Ervebo vaccine is available for Zaire Ebola virus, no proven or licensed vaccine exists for Bundibugyo virus disease, underscoring the need for new, species-specific vaccine and therapeutic trials.
According to WHO briefings and external reports, doses of the ChAdOx1 Bundibugyo vaccine could be ready for clinical trials within two to three months, while the rVSV Bundibugyo candidate may take approximately seven to nine months to reach trial readiness. WHO and collaborating scientists have stressed that the effectiveness of these new products is not yet known, making formal clinical trials essential both to manage the current outbreak and to build an evidence base for future responses.
