Does the Ebola vaccine being tested in DR Congo protect against the strain in Kenya?

Nobody knows yet. Ervebo, the vaccine now entering a trial in the Democratic Republic of Congo (DRC), is licensed only against Ebola virus (the Zaire species), not against Bundibugyo virus, the species in Kenya's cluster. The World Health Organization (WHO) said in guidance dated 31 August 2026 that some findings point to “possible cross-protection”, but that the evidence “remains insufficient to determine whether Ervebo® provides clinically meaningful protection in humans”.

The trial is called Tumaini, Swahili for “hope”. The Coalition for Epidemic Preparedness Innovations (CEPI), which funds two Bundibugyo-specific vaccine candidates, said the first participant was vaccinated on 23 October 2026 in Bunia, DRC. The trial is registered as NCT07842107 and co-sponsored by the DRC's Institut National de Recherche Biomédicale (INRB) and the University of Antwerp.

Tumaini is a Phase 2/3 adaptive trial: several candidate vaccines are tested side by side under one protocol, for safety, immune response and protection. It uses ring vaccination, which targets contacts at high risk of infection. Ervebo is the first candidate. Two Bundibugyo-specific candidates, from Moderna and from the University of Oxford with the Serum Institute of India, are being prepared to join. Dr Richard Hatchett, CEPI's chief executive, said: “There is still no licensed vaccine against Bundibugyo virus”.

Ebola is a group of related viruses, not one. WHO's Ebola fact sheet says six species have been identified, three of which cause large outbreaks: Ebola virus, Sudan virus and Bundibugyo virus. The vaccines it lists as approved, Ervebo (Merck & Co.) and Zabdeno and Mvabea (Janssen Pharmaceutica), are for Ebola virus disease only. The sheet says there is no approved vaccine or treatment for other Ebola diseases, including Bundibugyo virus disease.

The proof that Ervebo works against the Zaire species comes from Guinea. The Lancet published the trial's final results in its 4 February 2017 issue (doi:10.1016/S0140-6736(16)32621-6). It was an open-label, cluster-randomised ring vaccination trial: rings of contacts and contacts of contacts were assigned 1:1 to immediate vaccination or vaccination 21 days later. In the randomised part, 4,539 people in 51 immediate rings and 4,557 in 47 delayed rings were enrolled. From 10 days after randomisation, the immediate rings had no cases; the delayed rings had 16, in seven rings. Vaccine efficacy was 100% (95% confidence interval 68.9 to 100.0, the range of values the data support).

For Bundibugyo virus there are no such human results. The nearest evidence is from monkeys. In a 2011 study in the Journal of Infectious Diseases (doi:10.1093/infdis/jir350), macaques were given a vaccine built on a recombinant vesicular stomatitis virus (rVSV), the same platform as Ervebo, carrying Zaire's surface protein. With one dose, three of four animals (75%) survived challenge with Bundibugyo virus. With a vaccine based on the Côte d'Ivoire species, one of three survived, against one of four mock-vaccinated animals. The authors wrote that protection across species may need booster doses or several immunogens (the parts of a virus that trigger immunity).

WHO's August guidance says Ervebo's efficacy against Bundibugyo virus is unknown and that the vaccine should be used for it off-label only within research protocols. It asks for efficacy data to be generated quickly through a ring randomised controlled trial and for the uncertainty to be stated clearly. Dr Chikwe Ihekweazu, executive director of WHO's Health Emergencies Programme, said in CEPI's release: “The trial is an opportunity to generate the rigorous evidence needed to determine whether these vaccines can protect people at risk.”

In Kenya, the Ministry of Health said on 23 October that a 65-year-old woman, a close relative of the first patient, had died, bringing the toll to two deaths among nine confirmed cases. She had been placed in quarantine and developed symptoms on 13 October. The other seven patients were being treated in two isolation facilities. All 135 contacts had been traced and quarantined as of 20 October, according to WHO, and the ministry said there was no evidence of community spread. It had said the same on 17 October, when the count stood at seven. On 26 October the count was still nine cases and two deaths; the ministry said 20 contacts had been released after 21 days without symptoms and 98 remained in quarantine.

In the DRC, government data released on 27 October put confirmed cases at 10,060 and deaths at 4,887, Al Jazeera reported. The outbreak was declared on 15 May 2026.

With no vaccine proven for this strain, WHO's fact sheet lists the measures that control an outbreak: isolating patients in a designated treatment centre, identifying and monitoring contacts for 21 days, safe and dignified burials, hygiene, and standard plus extra precautions for health workers. The incubation period, from infection to first symptoms, runs from 2 to 21 days.

Last checked: 28 October 2026.