No specific treatments or vaccines exist for the Bundibugyo strain of Ebola, the virus behind an escalating outbreak in the eastern Democratic Republic of Congo and Uganda, global health authorities have confirmed. The World Health Organisation (WHO) has declared the situation a Public Health Emergency of International Concern (PHEIC), warning that the numbers are likely to rise.
The outbreak, believed to have caused approximately 906 suspected cases and 223 suspected deaths in the DRC alone, has now spread into Uganda, where nine confirmed infections have been recorded. Across both countries, 134 confirmed cases have been logged, with 18 deaths among them. The Bundibugyo ebolavirus (BDBV) carries a significant fatality rate, reaching up to 40 percent, though previous outbreaks have ranged between 25 and 50 percent. The epicentre lies in the DRC’s Ituri, North Kivu and South Kivu provinces, where contact tracing is hampered by insecurity, poor infrastructure and limited healthcare capacity.
Unlike the more common Zaire strain—for which approved vaccines and treatments exist—no licensed medical interventions are available for Bundibugyo. The WHO has advised prioritising several experimental drugs, including antibodies, antivirals and vaccines, for both treatment and prevention, but most have not undergone human trials and would require emergency or compassionate-use authorisation before deployment.
Vaccine candidates in development
The WHO has identified the single-dose rVSV Bundibugyo vaccine, developed by the International AIDS Vaccine Initiative (IAVI), as the most promising candidate to prevent BDBV. Known as rVSVΔG/BDBV-GP, it uses the same technology as Merck’s approved Ervebo vaccine for the Zaire strain. A 2023 proof-of-concept study showed a survival benefit in non-human primates. The WHO said development of the vaccine would likely take seven to nine months before it is ready for assessment in a clinical trial. IAVI said it is advancing the candidate towards a trial and preparing for manufacturing, including transferring the vaccine virus and processes for Good Manufacturing Practices production.
A second vaccine candidate, ChAdOx1 Bundibugyo, is being developed by Oxford University and the Serum Institute of India. It is based on ChAdOx1 technology, which was used in the Oxford/AstraZeneca COVID-19 vaccine. The Serum Institute started production under an “emergency response framework” alongside the Coalition for Epidemic Preparedness Innovations (CEPI) and the University of Oxford as soon as it received word of the outbreak this month, a spokesperson said. Doses could be ready within two to three months for efficacy assessment through a clinical trial, the WHO said, adding that additional animal studies have yet to be conducted. The WHO noted experts considered a single dose potentially suitable for contacts of Ebola cases, while a two-dose regimen might be used for high-risk but unexposed groups, including healthcare workers and frontline responders. The Oxford Vaccine Group said it is working to generate pre-clinical data to support development and testing. CEPI, which funds early-stage outbreak vaccines and aims to have shots available within 100 days of an outbreak, said it is in talks with both candidates about speeding up development.
Merck’s Ervebo, the only licensed Ebola vaccine, is approved only for the Zaire strain, and its efficacy against Bundibugyo is limited and inconclusive. The WHO has recommended Ervebo not be used outside of carefully designed research settings for this outbreak.
Antibody and antiviral treatments under evaluation
Among antibody drugs, the WHO has recommended prioritising Mapp Biopharmaceutical’s pan-ebolavirus drug MBP134—a combination of two human monoclonal antibodies—for clinical trials among confirmed BDBV cases. Initially studied for the Sudan ebolavirus strain, MBP134 was found to be safe and well tolerated in early-stage trials. Its development has been backed by the U.S. Biomedical Advanced Research and Development Authority (BARDA). BARDA said it is coordinating shipments of the investigational treatment for potential use in high-risk Americans exposed to the virus. Mapp said MBP134 has shown similar activity against all known ebolaviruses and that it is working with the WHO and other authorities as part of the Congo response.
Regeneron Pharmaceuticals’ antibody drug candidate maftivimab is also being explored by the WHO. According to the company, it has been shown in a lab to be active against Bundibugyo Ebolavirus. Maftivimab is the most potent neutralizing antibody in Regeneron’s Inmazeb, a three-antibody cocktail approved by the U.S. Food and Drug Administration for treating Zaire Ebolavirus infection. Regeneron said it is working to prepare existing supply of maftivimab for use in upcoming clinical trials. It recently donated 500 doses of Inmazeb to the WHO, which could be used if found helpful, and added that “supply of Inmazeb is already on the ground in the DRC, should WHO wish to utilize it for immediate treatment or as an additional component of the study.”
Human monoclonal antibodies isolated from Bundibugyo survivors are also being investigated. One candidate, BDBV289-N, demonstrated efficacy in a 2018 animal study supported by the U.S. National Institutes of Health, showing up to 100 percent protection in infected monkeys even when treatment started up to eight days after infection.
On the antiviral front, Gilead Sciences’ experimental oral drug obeldesivir is being considered by the WHO as a potential post-exposure treatment to prevent exposed individuals from developing disease. A once-daily 10-day course provided up to 100 percent protection in monkeys against Zaire and Sudan Ebola strains when started 24 hours after exposure. A company spokesperson said obeldesivir “is predicted to be active against this particular (Bundibugyo) strain” and that preclinical data shows positive results. The WHO has indicated this could be the first prophylaxis drug trial during an Ebola outbreak.
Gilead’s intravenous antiviral remdesivir has shown activity against the Bundibugyo virus in laboratory studies conducted by researchers at the University of Texas Medical Branch, with some data suggesting it may have stronger activity against BDBV than against the Zaire strain. The WHO has also recommended evaluating a combination therapy using a monoclonal antibody and remdesivir.
Another experimental broad-spectrum antiviral, NV-387 from Nanoviricides Inc., is ready for a potential Phase II trial. The drug mimics host heparan sulfate proteoglycan, a molecule many viruses depend on for cell infection.
Diagnostic testing
The WHO indicated that limited testing capacity for the Bundibugyo strain has slowed the response to the outbreak. Several diagnostic tests are available. BioFire Defense, an affiliate of French diagnostic firm bioMérieux, makes an FDA-cleared test—the BioFire Global Fever Special Pathogens Panel—that can detect multiple Ebola species, including Bundibugyo. A company spokesperson said it is increasing production capacity and engaging with public health stakeholders to assess potential needs.
Germany-based Altona Diagnostics’ RealStar Filovirus Screen RT-PCR Kit 1.0 is being used in Congo to detect the current outbreak. The firm has ramped up production to support local testing facilities. Altona also produces a research-use-only kit, the RealStar Filovirus Type RT-PCR Kit 2.0, which can differentiate between the five Ebolavirus species. Other available tests include Cepheid’s GeneXpert Ebola and Xpert Edge X Hemorrhagic Fever panel, and OraSure’s OraQuick Ebola immunoassay, which can test whole blood and cadaveric oral fluid samples. The U.S. Centers for Disease Control and Prevention (CDC) is providing technical assistance with surveillance, contact tracing, infection prevention and control, and coordination with international partners.