When an Ebola outbreak linked to the Bundibugyo strain emerged in eastern Democratic Republic of Congo this spring, global health authorities faced an urgent problem: unlike the better-known Zaire strain, there were no approved vaccines or treatments ready to deploy. Nearly 750 suspected cases and 177 deaths have been reported so far, with the World Health Organization warning that numbers are likely to climb—and with a fatality rate of up to 40%, speed matters.
The stakes are high enough that researchers and pharmaceutical companies around the world are moving with unusual urgency. Several experimental vaccines and therapies are being assessed in parallel, racing to see which might contain the outbreak before it grows further. Most have never been tested in humans, meaning they would need emergency authorization to be used in the DRC. But the calculus is simple: no options exist otherwise.
On the vaccine front, researchers at the University of Texas Medical Branch have developed a Bundibugyo-specific vaccine called rVSVΔG/BDBV-GP using the same technology behind Merck's approved Zaire Ebola vaccine, Ervebo. A 2023 proof-of-concept study showed survival benefits in non-human primates, and discussions are underway to advance it further—the WHO estimates it could take six to nine months to manufacture doses. Meanwhile, the Serum Institute of India has already begun producing another candidate, ChAdOx1 BDBV, under an emergency response framework. Based on the same technology used in the Oxford/AstraZeneca COVID-19 vaccine, doses could be ready within two to three months, though animal studies still need to be completed first. The Coalition for Epidemic Preparedness Innovations, which funded early COVID-19 vaccines and aims to deliver shots within 100 days of an outbreak, is coordinating with both candidates to accelerate development.
On the treatment side, three different approaches are being explored. Mapp Biopharmaceutical is developing MBP134, a pan-ebolavirus antibody drug that showed safety and tolerability in early trials for Sudan Ebolavirus and has demonstrated similar activity against all known Ebola strains. The U.S. Biomedical Advanced Research and Development Authority is coordinating shipments for potential use with high-risk Americans. Regeneron Pharmaceuticals' maftivimab, which has shown laboratory activity against Bundibugyo, is being considered by the WHO—the company recently donated 500 doses of Inmazeb, an approved Zaire treatment combining maftivimab with two other antibodies, though its efficacy against Bundibugyo remains uncertain. A third approach involves human monoclonal antibodies isolated directly from Bundibugyo survivors. One candidate, BDBV289-N, demonstrated striking results in a 2018 animal study: it provided up to 100% protection in infected monkeys, even when treatment began eight days after infection.
Complementing these efforts, Gilead Sciences is exploring two antivirals. Their experimental oral drug obeldesivir provided up to 100% protection against Zaire and Sudan strains in monkey studies when given within 24 hours of exposure, and the WHO is considering it as a post-exposure preventative. Gilead's remdesivir, already used against other viruses, has shown activity against Bundibugyo in laboratory studies conducted at the University of Texas Medical Branch, with some data suggesting it may be more effective against this strain than against Zaire.
The outbreak has crystallized a paradox of global health: multiple promising tools exist on the shelf, but none are yet licensed for use. The race now is to prove them safe and effective in time to matter.