WHO prioritizes three therapeutics and two vaccine candidates for Bundibugyo Ebola trials

An outbreak of Bundibugyo virus—a rare form of Ebola—is spreading across the Democratic Republic of the Congo and into Uganda, and the world has no approved medicines or vaccines to fight it. In response, the World Health Organization convened its top advisory groups to identify which experimental treatments and preventive tools show enough promise to move into human trials. The stakes are high: there is no time for the usual pace of drug development, but there is also no room for error. Everything tested must happen inside carefully controlled clinical trials, under the strictest ethical oversight.

The WHO's expert panels settled on five candidates worth pursuing. For treating people already infected with Bundibugyo virus disease, three therapeutics rose to the top: two monoclonal antibodies called MBP134 and Maftivimab, and an antiviral drug called remdesivir. The experts also recommended testing a combination approach—pairing one of the antibodies with remdesivir—to see if two drugs working together might work better than one alone. These are not new molecules. Remdesivir has been used against other viral outbreaks. The monoclonal antibodies are engineered proteins designed to neutralize the virus. But whether they will work against Bundibugyo specifically remains unknown. That is precisely why they must be tested.

For prevention, the picture is more complex. One approach involves giving an oral antiviral called obeldesivir to people who have been exposed to someone with confirmed Bundibugyo disease—a strategy called post-exposure prophylaxis. The idea is straightforward: if you can reach contacts quickly enough and give them the drug, you might prevent infection before it takes hold. But this depends entirely on effective contact tracing, and in some areas of the Congo, that infrastructure is fragile or absent. The drug itself is promising; the logistics are the real challenge.

Two vaccine candidates also made the priority list. The first is a single-dose vaccine based on a virus called rVSV, modified to carry Bundibugyo genetic material. It is being developed by the International AIDS Vaccine Initiative and will likely need seven to nine months of additional work before it can enter clinical trials. The second is ChAdOx1 Bundibugyo, developed by Oxford University and the Serum Institute of India, which could potentially be ready for testing in two to three months—though researchers still need more animal data to confirm it is safe enough to move forward. This second vaccine could be given as a single dose to contacts of infected people, or as two doses to health workers and other high-risk groups who have not yet been exposed.

There is one licensed Ebola vaccine already in existence: Ervebo. It works against the most common form of Ebola found in Africa. But Bundibugyo is different, and evidence that Ervebo offers any protection against it is thin and inconclusive. The WHO is explicit: Ervebo should not be used outside of carefully designed research settings, where its actual performance against Bundibugyo can be measured. Using it without that data would be both ethically questionable and scientifically wasteful.

The WHO, the governments of the Congo and Uganda, the Africa Centres for Disease Control, and a network of scientific partners are now working together to design and implement the clinical trials that will test these candidates. The work must meet the highest ethical standards, with national health authorities leading and affected communities consulted at every step. But the organization is also clear about what comes first: the traditional tools that have worked for decades of Ebola responses—surveillance, rapid testing, contact tracing, isolation, infection control, community engagement, and safe burials. Those remain the backbone of outbreak response. The new drugs and vaccines, when they arrive, will be additions to that foundation, not replacements for it.