Can two new vaccines help turn the tide against Bundibugyo Ebola?
Two experimental Ebola vaccines are set to join a crucial trial in the Democratic Republic of the Congo as the Bundibugyo virus disease outbreak there continues.
- 10 November 2026
- 7 min read
- by Linda Geddes
At a glance
- Two experimental vaccines have been recommended by World Health Organization experts for inclusion in the ongoing Phase 2/3 Tumaini trial in the Democratic Republic of the Congo, as the country battles a major outbreak of Bundibugyo virus disease.
- The University of Oxford’s ChAdOx1 BDBV vaccine and Moderna’s mRNA-1469 vaccine are expected to join Ervebo, an existing Ebola vaccine whose effectiveness against Bundibugyo virus is not yet known.
- The trial is using a strategy called ring vaccination, where people who have been in contact with confirmed Ebola cases are offered a vaccine, to assess whether any of the candidates can protect against severe disease and/or death caused by Bundibugyo virus.
Two experimental vaccines against Bundibugyo virus (BDBV) virus are set to join an ongoing trial in the Democratic Republic of the Congo (DRC), where researchers are already investigating whether an existing Ebola vaccine (against a different species of Ebola virus) offers any cross-protection against the Bundibugyo virus disease.
The recommendation by World Health Organization (WHO) experts marks a significant step towards developing effective vaccines against Bundibugyo virus, which is driving the ongoing Ebola outbreak in DRC – now the second largest Ebola outbreak in history. As of 7 November 2026, nearly 11,000 cases and more than 5,300 deaths had been recorded in DRC, with further imported cases detected in other countries.
But what makes these vaccines promising, how will researchers establish whether they work and what could happen next?
Why is a vaccine against Ebola caused by Bundibugyo virus needed?
Bundibugyo virus is one of four viruses known to cause Ebola disease in humans. It was first identified in 2007 and has caused two previous outbreaks of Ebola. However, until the current outbreak it had been considered a rare disease and researchers had prioritised the development of vaccines and other countermeasures against Ebola virus (formerly known as Zaire ebolavirus) instead. It has been responsible for most previous Ebola outbreaks, including the 2014–2016 West Africa outbreak.
Although an effective vaccine against Ebola virus now exists, there is currently no licensed vaccine targeting Bundibugyo virus.
Named after the Swahili word for ‘hope’, the Tumaini trial aims to establish whether the existing Ebola vaccine, Ervebo, or new experimental Bundibugyo specific vaccines can safely and effectively protect people against acquiring Bundibugyo virus disease.
Which experimental vaccines are being included in the trial?
So far, two experimental Bundibugyo vaccine candidates have met WHO’s criteria for inclusion in the trial. They are the ChAdOx1 BDBV vaccine, developed by the University of Oxford in collaboration with the Serum Institute of India, and mRNA-1469, developed by Moderna. These vaccine candidates use different technologies to stimulate immune responses against Bundibugyo virus.
ChAdOx1 BDBV uses a harmless, modified chimpanzee adenovirus to deliver genetic instructions for producing a protein found on the surface of Bundibugyo virus. MRNA-1469 uses messenger RNA (mRNA) to deliver similar instructions, packaged inside tiny lipid (fat) particles. In both cases, the aim is to trigger immune responses that can recognise and fight the virus if a vaccinated person is subsequently exposed.
Both candidates have shown encouraging results in animal studies, while early clinical trials in the UK and Canada have suggested that they can safely stimulate immune responses in humans. Subsequent phase 1 trials are currently being planned or are recruiting participants in Uganda.
The safety and effectiveness of the technologies underpinning these vaccines was also demonstrated during the COVID-19 pandemic: Oxford’s COVID-19 vaccine used the same modified chimpanzee adenovirus platform as its Bundibugyo candidate, while Moderna’s COVID-19 vaccine used the same underlying mRNA technology. Billions of doses of these vaccines have been administered worldwide, providing insights into their safety profiles and ability to protect against disease.
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“Evaluating vaccines specifically designed against Bundibugyo virus during an outbreak is an important scientific milestone,” said Dr Meg Doherty, Director of Science for Health at WHO. “WHO’s Technical Advisory Group on Candidate Vaccine Prioritization provided an independent assessment of the early safety and immunogenicity data of these two vaccines and recommended moving them forward to Phase 2/3 evaluation.
“The Tumaini platform trial gives us a unique opportunity to generate rigorous evidence, in real time, on whether these candidates can safely protect people from this deadly disease. It shows what is possible when science is embedded in an outbreak response, bringing researchers, countries and partners together to develop the tools we urgently need.”
Both vaccine candidates will enter the trial following national approvals. Results from the trial are expected in early 2027, WHO said.
How will these Bundibugyo vaccine candidates be tested?
The Tumaini trial will use a ring-guided vaccination strategy to test whether any of these vaccines can prevent disease caused by Bundibugyo virus. This involves vaccinating people who have been in contact with someone who became ill or died from Ebola, and are therefore at increased risk themselves. The approach was used during the campaign to eradicate smallpox and later adapted by WHO and partners to test the effectiveness of the Ervebo vaccine during the West Africa Ebola outbreak of 2014–2016.
Participants will be randomly assigned to receive either an Ebola vaccine or a comparator vaccine, then monitored for signs of disease, with prompt hospital treatment provided to anyone who falls ill. On day 29, participants will receive the alternative vaccine, meaning everyone will have the opportunity to be vaccinated against Ebola. Neither the participants nor the healthcare staff and researchers involved in the trial will know which vaccine was given first.
The trial is also designed to be flexible, meaning further vaccine candidates could be added, or existing ones dropped, if emerging evidence suggests they are unlikely to be effective. An independent committee will review the evidence as it accumulates during the trial.
What else is being done to prepare for the roll-out of a Bundibugyo vaccine?
Even if one of the vaccines proves effective, ensuring sufficient doses are available for use during the current outbreak, and future ones, presents a further challenge. Because Bundibugyo outbreaks are rare and unpredictable, manufacturers have little incentive to invest in developing vaccines or producing them at scale. To help overcome this problem, Gavi, the Vaccine Alliance, and the Coalition for Epidemic Preparedness Innovations (CEPI) have launched a joint “push-pull” financing strategy to accelerate vaccine development and manufacturing.
The “push” comes from CEPI, which has committed more than US$ 75 million to support the development and testing of several Bundibugyo vaccine candidates, including manufacturing doses for clinical trials. These include the Oxford and Moderna candidates.
The “pull” comes from Gavi, which has approved up to US$ 40 million to help manufacturers invest in larger-scale production before they know whether their vaccines will be successful, meaning doses could be deployed rapidly, should clinical trials produce positive results.
Once sufficient safety and efficacy data is available for a policy recommendation, WHO is expected to grant Emergency Use Listing (EUL) and/or Prequalification, key milestones required for broader deployment of any Bundibugyo vaccine.
“The recommendation to add these two new Ebola vaccine candidates to the Tumaini trial is an exciting development, which we hope will bring the world closer to a vaccine that could help end the current Bundibugyo outbreak, and stop future outbreaks in their tracks,” said Emanuele Capobianco, Gavi’s Director of Global Health Security.
"Our surge financing aims to ensure that vaccine doses will be ready to go, and countries will be able to access them quickly, should this trial show any candidate to be effective.
“Longer-term, we hope to build a global stockpile of Bundibugyo virus vaccines, just as we have for Ebola virus vaccine, strengthening global health security and protecting communities against these devastating viruses.”
The Gavi-funded Ebola vaccine stockpile framework allows for the inclusion of vaccines against different Ebola virus species, enabling its composition to evolve as the vaccine landscape develops. While the current stockpile consists of vaccines against Zaire ebolavirus, vaccines protecting against Bundibugyo virus could be incorporated as they become available, subject to available funding and relevant policy and programmatic recommendations.
