WHO fast-tracks candidate vaccines and therapeutics for Bundibugyo virus outbreak

An outbreak of Bundibugyo virus—a species of Ebola—is spreading across the Democratic Republic of the Congo and into Uganda. The World Health Organization has no licensed drugs or vaccines to fight it. So in May, the agency convened its expert advisory groups to identify which experimental treatments and preventive tools show enough promise to move into human trials, and fast.

The situation is urgent but the path forward is constrained. There are no approved therapeutics or vaccines for Bundibugyo virus disease. What exists are candidates—compounds that laboratory and animal data suggest might work. The WHO's advisory groups, including its R&D Blueprint technical teams and its Strategic Advisory Group of Experts on Immunization, reviewed these prospects and made their recommendations with a single condition: all of them must be tested only within formal clinical trials. No emergency use outside research protocols. The goal is to generate solid evidence while protecting participants and maintaining ethical rigor in the midst of an active outbreak.

For treating people already infected, the experts identified three drugs worth prioritizing. Two are monoclonal antibodies—MBP134 and Maftivimab—which work by helping the immune system recognize and attack the virus. The third is remdesivir, an antiviral that interferes with the virus's ability to replicate. The advisory groups also recommended testing a combination approach: a monoclonal antibody paired with remdesivir together. These treatments would be evaluated in clinical trials among confirmed cases in the affected countries.

Prevention is more complicated. For people exposed to confirmed cases—household members, healthcare workers, contacts identified through tracing—the experts recommended prioritizing obeldesivir, an oral antiviral taken as tablets after exposure to prevent infection. But this approach depends on something that remains operationally difficult in parts of the Congo: effective contact tracing. If you cannot find and monitor the contacts, you cannot give them the drug in time.

Two vaccine candidates emerged as most promising. The first is a single-dose vaccine based on rVSV technology, being developed by the International AIDS Vaccine Initiative. It targets Bundibugyo specifically and could be ready for clinical trial assessment in seven to nine months. The second, ChAdOx1 Bundibugyo, developed by Oxford University and the Serum Institute of India, could potentially be available within two to three months—though it still needs additional animal data to confirm its safety profile. Experts noted that the ChAdOx1 vaccine might work as a single dose for contacts of cases, or as a two-dose regimen for high-risk groups like healthcare workers who have not yet been exposed.

There is one licensed Ebola vaccine already in use: Ervebo. It works against the most common Ebola virus species in Africa. But Ervebo is not approved for Bundibugyo, and evidence that it provides cross-protection against other Ebola species is limited and inconclusive. The WHO recommends against using it outside carefully controlled research settings, where its actual performance against Bundibugyo can be measured.

The WHO, the governments of the Democratic Republic of the Congo and Uganda, the Africa Centres for Disease Control and Prevention, and other scientific partners are now working to design and implement clinical trial protocols that meet the highest ethical standards. All research must be led by national health authorities and conducted in close consultation with affected communities. The immediate priority, however, remains the tools that have worked for decades: surveillance, rapid testing, contact tracing, patient isolation and care, infection prevention, community engagement, and safe burial practices. The experimental drugs and vaccines are the future. For now, the outbreak must be contained with what is known to work.