Licensed for Zaire, Tested on Bundibugyo: Congo Starts Its Ebola Trial

The Democratic Republic of the Congo has begun a vaccine trial against Bundibugyo Ebola, testing whether a shot licensed for another Ebola species can help stop the outbreak. ^[1]

The first participant received Merck's Ervebo on October 23, 2026, in Bunia, in eastern Congo. The trial, called Tumaini, begins amid the largest recorded Bundibugyo outbreak, with 9,552 confirmed cases and 4,602 deaths in the country as of October 21, according to the Coalition for Epidemic Preparedness Innovations, or CEPI, which funds and supports the work. ^[1]

Ervebo is licensed against Ebola virus, also known as the Zaire species. The virus driving this outbreak is Bundibugyo, a different species for which no vaccine is licensed. Whether Ervebo can protect people against it is the question the trial must answer. ^[1][5]

Laboratory and animal findings suggest possible protection across the two species, according to the World Health Organization. But WHO says that evidence is insufficient to establish meaningful protection in humans and recommends using Ervebo against the current outbreak only within a research protocol. ^[3][5]

Vaccines designed specifically for Bundibugyo, developed by Moderna and by the University of Oxford with the Serum Institute of India, are also being prepared to enter Tumaini. Ervebo is the first candidate being given to participants, according to CEPI's October 23 announcement. ^[1]

A licensed vaccine, an unanswered question

Ervebo's existing approval makes it an available candidate, not an established defence against this outbreak. Its licence concerns a particular Ebola species, and the protection demonstrated against that species cannot simply be assumed for Bundibugyo. WHO's recommendation puts that uncertainty at the centre of how the vaccine should be used. ^[3][5]

The practical response has two parts: make doses available and test whether they work. Congo requested Ervebo from the global stockpile, and WHO and Africa CDC announced an initial allocation of 70,000 doses. Of those, 20,000 were allocated for a Phase 3 trial and 50,000 for frontline and health workers under WHO advisory recommendations. ^[4]

Those are allocations, not a count of vaccinations completed. They also do not establish protection for the people offered the vaccine. ^[4][5]

WHO says recipients should be told about its benefits, risks and limitations, and should give informed consent. Vaccination must not replace other recommended measures against Bundibugyo disease. ^[4][5] A familiar product name must not obscure that Ervebo is licensed for the Zaire species, with its benefit against Bundibugyo still being tested.

CEPI chief Richard Hatchett said the absence of a licensed Bundibugyo vaccine has a daily cost in lives lost and in health workers going to work without protection. That is the urgency behind the trial, and the reason its results matter beyond the research teams. ^[1]

Testing protection where transmission is happening

Tumaini is led by Congo's Ministry of Health, with the Institut National de Recherche Biomédicale, the country's biomedical research institute, and the University of Antwerp as co-leads and co-sponsors. It is a Phase 2/3 adaptive platform trial, a framework that allows researchers to assess vaccine candidates and add others as they become ready. ^[1]

Its stated aims cover safety, immune response and efficacy. Those are separate questions: whether a vaccine causes harmful effects, whether the body responds to it, and whether it actually protects people against disease. The last question is the one that determines how much a vaccination programme can contribute to controlling this outbreak. ^[1]

The trial uses ring vaccination, focusing on people at high risk through contact with cases. This approach directs research towards the people facing exposure rather than spreading doses across a population without regard to contact with the virus. ^[1][2]

WHO says a well-designed ring randomized controlled trial is the most rigorous and reliable way to assess Ervebo's efficacy against Bundibugyo. Randomized comparisons allow researchers to judge whether differences in disease outcomes reflect vaccination rather than differences between the people being compared. ^[3][5]

The first injection starts that work. Establishing protection requires results from participants over time, not simply evidence that doses have been delivered. ^[3][5]

The announced launch does not specify enrolment numbers, the detailed comparisons between candidate groups, follow-up periods or when interpretable results will be ready. Nor does it establish a date when either Bundibugyo-specific candidate will begin being administered in Tumaini. ^[1]

Research alongside the emergency response

The trial has to operate within an active outbreak response. Steve Ahuka-Mundeke, Congo's Ebola response incident manager, said it must be coordinated with frontline work, with stopping transmission and saving lives the priority. ^[1]

That coordination matters because research and outbreak control have different immediate tasks. Researchers need reliable comparisons. Response teams need to interrupt transmission now. WHO's instruction to maintain other protective measures keeps the experimental vaccination programme from displacing measures recommended for the disease. ^[4][5]

The platform design gives Tumaini room to test more than the first available option. CEPI said on October 13 that the Moderna and Oxford-Serum Institute candidates were in Phase 1 trials, the early stage of testing in people. Its October 23 announcement said preparations were underway for both to join Tumaini shortly. ^[1][2]