WHO adds two Bundibugyo vaccines to Ebola trial in the DRC

Two experimental vaccines made to fight a type of Ebola virus that is behind the outbreak in the Democratic Republic of the Congo (DRC) will be added to the country's Tumaini clinical trial, the World Health Organization (WHO) said in a recent news release. The vaccines—ChAdOx1 BDBV, which comes from the University of Oxford and the Serum Institute of India, and Moderna's mRNA-1469—were added to combat Bundibugyo.

A WHO advisory group recommended both vaccines for more testing this week, based on lab, animal and early human data. They will join the trial once national approvals are in place. WHO said this is the first time vaccines built for the Bundibugyo virus will be tested during an outbreak.

“Vaccines alone will not end this outbreak, but they could become a powerful new tool for bringing it under control,” Tedros Adhanom Ghebreyesus, Ph.D., WHO director-general, said in the release.

What is Bundibugyo virus disease?

Three viruses are known to cause large Ebola outbreaks: Ebola virus (often called the Zaire type), Sudan virus and Bundibugyo virus, according to the WHO Ebola fact sheet. Fruit bats are thought to carry the viruses in nature. People catch it through direct contact with an infected person's blood or body fluids, or with surfaces those fluids have touched. People can't spread it before they have symptoms.

Symptoms show up 2 to 21 days after infection and often start suddenly. Early signs include fever, fatigue, muscle pain and headache. After, patients may have vomiting, diarrhea, rash and kidney and liver problems. On average, about half of people with Ebola die, WHO says, though past outbreaks have ranged from 25% to 90%.

Bundibugyo virus was first found in 2007 in the Bundibugyo district of western Uganda. A second outbreak hit the DRC in 2012, according to the UK Health Security Agency. The current outbreak began in May. It is now the largest Bundibugyo outbreak on record and the second-largest Ebola outbreak ever. As of late October, the DRC had reported 10,193 confirmed cases and 4,960 deaths across eight provinces, according to the European Centre for Disease Prevention and Control (ECDC). Cases tied to the outbreak have also turned up in Kenya and Nigeria.

According to the release, there is a major gap in tools to fight it. The approved Ebola vaccines—Ervebo (Ebola Zaire vaccine) and the two-dose Zabdeno (Ad26.ZEBOV) and Mvabea (MVA-BN-Filo) regimen—work only against the Zaire type. The same is true of the two approved antibody treatments, Ebanga (ansuvimab-zykl) and Inmazeb (atoltivimab, maftivimab and odesivimab-ebgn).

How the Tumaini Ebola vaccine trial works

Meaning "hope" in Swahili, the Tumaini phase 2/3 trial gave its first shot in late October in Bunia, the capital of Ituri province and the center of the outbreak, the Coalition for Epidemic Preparedness Innovations (CEPI) said in a news release. Ervebo was the first vaccine tested to see whether it also protects against Bundibugyo.

The trial can test several vaccines under one plan. It uses ring vaccination, which means vaccinating the contacts of people with confirmed cases. A similar trial in Guinea about a decade ago proved Ervebo worked against the Zaire type. Four vaccination rings are in place, and more are being set up.

The DRC's Institut National de Recherche Biomédicale and Belgium's University of Antwerp lead the trial. WHO, Médecins Sans Frontières and other groups are partners, and CEPI is funding vaccine development.

“There is still no licensed vaccine against Bundibugyo virus, and the cost of that absence is being counted in the DRC every day, in lives lost and in health workers who go to work without protection” Richard Hatchett, M.D., CEO of CEPI, said when the trial launched.

Treatment research for Bundibugyo virus disease

Researchers are also testing treatments. The WHO-sponsored PARTNERS trial, which began in July, is studying whether patients are more likely to survive if they get the experimental antibody MBP134, the antiviral Veklury (remdesivir) or both. Maftivimab, one of the three antibodies in Inmazeb, will soon be added to the trial. A separate study, EBO-PEP, is testing whether an experimental antiviral pill, obeldesivir, can keep high-risk contacts from getting sick.

Early results from the treatment trial are expected in the coming months, and vaccine results are expected in early 2027, WHO said. Tedros called the vaccines' readiness for testing “a testament to the power of science and partnership.”