DR Congo tests Zaire-strain Ebola vaccine against Bundibugyo outbreak

Overview

Updated 2 hours ago

Congo's health workers are getting the only Ebola vaccine that exists at scale — even though it was built for a different virus. Vaccinations began September 19 in Bunia, the epicenter of the country's deadliest outbreak, where a 20,000-person study will test whether the Ervebo shot protects against the Bundibugyo strain.

Bundibugyo has no licensed vaccine or treatment. With 7,541 confirmed cases and 3,639 deaths, the outbreak is already the deadliest of Congo's 17 recorded Ebola outbreaks, and the World Health Organization says it's on track to surpass the 2014-2016 West Africa epidemic, which killed more than 11,000 people.

Why it matters

With no licensed Bundibugyo vaccine, this study decides whether Congo's only Ebola shot helps — or leaves 20,000 frontline workers exposed.

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Key Indicators

7,541

Confirmed Ebola cases

As of September 19, 2026, per DRC health authorities.

3,639

Deaths

A 48.3% fatality rate, the highest of any Congo outbreak.

20,000

Frontline workers in BRAVO study

Health workers in Ituri and North Kivu provinces, the highest-risk group.

70,000

Ervebo doses allocated to DRC

From the global Ebola vaccine stockpile, coordinated by the WHO.

48.3%

Case fatality rate

3,639 deaths among 7,541 confirmed cases.

Voices

Curated perspectives — historical figures and your fellow readers.

Ever wondered what historical figures would say about today's headlines?

People Involved

Dr. Guyguy Manangama

Epidemiologist and deputy director of operations, MSF

Overseeing the BRAVO vaccination study

Organizations Involved

Médecins Sans Frontières and Epicentre

International medical humanitarian organization and its research arm

Operators of the BRAVO vaccination study

MSF, with its epidemiological research center Epicentre, designed and runs the study evaluating Ervebo among frontline workers.

World Health Organization

United Nations health agency

Coordinating the outbreak response and vaccine supply

The WHO runs the training center in Bunia where vaccinations began and coordinates the global Ebola vaccine stockpile.

Merck & Co.

Pharmaceutical company

Manufacturer of the Ervebo vaccine

Merck developed Ervebo, the only Ebola vaccine available at scale, produced in Germany.

Timeline

2 events Latest: Today

September 2026
Rollout reported as death toll passes 3,600
Today Public Health

Confirmed cases hit 7,541 with 3,639 deaths; WHO warns the outbreak could surpass the 2014-2016 record.
Today
BRAVO vaccination study launches in Bunia
Public Health

MSF and Epicentre start vaccinating 20,000 frontline workers in Ituri and North Kivu against the Bundibugyo strain.
Yesterday

Scenarios

Study shows Ervebo protects against Bundibugyo

Uncertain Resolves by Q3 2027

Discussed by: MSF epidemiologist Guyguy Manangama, who noted preliminary data suggest partial protection; Epicentre researchers

Interim or final BRAVO data show vaccinated frontline workers had significantly lower infection or severe-disease rates than unvaccinated comparison groups. That would support expanding vaccination beyond the initial 20,000 workers and give health authorities a working tool for this outbreak and future Bundibugyo events.

Bundibugyo-specific vaccine reaches the field

Possible Resolves by Q2 2027

Discussed by: MSF, which states several Bundibugyo-targeting vaccines are in development and may be available in coming months

A vaccine developed specifically for the Bundibugyo strain clears clinical trials or receives emergency authorization and begins rollout in the DRC. This would make the Ervebo experiment moot and give Congo a purpose-built tool, though it depends on trials moving faster than the outbreak.

Outbreak becomes deadliest on record

Possible Resolves by End of 2027

Discussed by: World Health Organization, which says the outbreak is on track to surpass the 2014-2016 West Africa epidemic

The outbreak continues spreading into underprepared areas amid insecurity, displacement, a health workers' strike, and intense population movement. If cumulative deaths exceed the roughly 11,300 from West Africa, it becomes the deadliest Ebola outbreak ever recorded — driven by the complete absence of a proven countermeasure for this strain.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

August - December 2007

Bundibugyo outbreak, western Uganda (2007)

The Bundibugyo strain was first identified in Uganda's Bundibugyo district. The outbreak was smaller and less deadly than Zaire-strain epidemics, and it had no licensed vaccine or treatment. The strain reappeared only rarely afterward.

Then

The outbreak was contained with basic infection control, and nearly two decades passed with little research into a Bundibugyo-specific vaccine.

Now

The strain's rarity left the world unprepared for a large-scale emergence.

Why this matters now

This is Bundibugyo's first major return, and the lack of preparedness is why Congo is testing a Zaire-strain vaccine against it.

December 2013 - June 2016

West Africa Ebola epidemic (2014-2016)

The deadliest Ebola outbreak on record killed more than 11,000 people, mostly in Guinea, Liberia, and Sierra Leone. Caused by the Zaire strain, it drove crash-development of the vaccine that became Ervebo, tested in a 2015 ring-vaccination trial in Guinea that showed near-perfect protection.

Then

The Guinea trial gave the world its first effective Ebola vaccine and established ring vaccination as the standard response strategy.

Now

Ervebo received regulatory approval and became the default tool for every subsequent outbreak.

Why this matters now

The WHO warns the current Bundibugyo outbreak is on track to surpass this death toll — but without a proven vaccine for its strain.

August 2018 - June 2020

North Kivu Ebola outbreak (2018-2020)

The second-deadliest Ebola outbreak on record, centered in the same eastern Congo provinces now affected. Ervebo was deployed at scale in an active outbreak for the first time, vaccinating hundreds of thousands of people before the outbreak was declared over.

Then

More than 2,000 people died despite the vaccine, but mass vaccination plus community engagement ultimately contained the Zaire-strain epidemic.

Now

It became the playbook for outbreak response in the region.

Why this matters now

This is the template MSF and the WHO are following now — but the strain is different, the one variable the playbook doesn't cover.