Ebola: Why is there still no vaccine for the Bundibugyo strain?

The Democratic Republic of Congo finds itself at the center of a major health crisis as an Ebola outbreak emerges, driven by the less common Bundibugyo type of the genus Orthoebolavirus. This development has reignited global questions about why there is still no vaccine for a pathogen that has been known for decades.

Historically, the first scientifically documented Ebola epidemic occurred in 1976 near the Ebola river in Zaire, now the DRC. The specific Bundibugyo strain was later identified during a 2007 outbreak in Uganda, followed by another outbreak in the DRC in 2012. Torsten Feldt, a doctor of tropical medicine at Düsseldorf's University Hospital, noted that having encountered this virus twice before, sufficient time was available to develop vaccines and therapeutic options, but crucial preparation time was lost.

From an immunological standpoint, experts point out that Ebola is a very worthwhile candidate for a vaccine compared to mutating pathogens like influenza or HIV. Leonie Mayer from the German Center for Infection Research suggests that developing a vaccine against Bundibugyo should be relatively straightforward. However, vaccines cannot be developed as a precautionary measure against every potential pathogen due to funding limitations and the prioritization of other strains, such as the Sudan Ebola virus.

Furthermore, the existing licensed vaccine, Ervebo, was developed specifically for the Zaire variant, leaving no approved protection for other strains. While a recent study led by Mayer found cross-reactive T-cell responses against Bundibugyo using the licensed vaccine, researchers remain uncertain whether this immune response provides actual protection or just a milder disease progression. Deploying vaccines without proven efficacy poses ethical challenges and risks creating a false sense of security or damaging public trust during an epidemic.

Delays in developing a vaccine for the Bundibugyo strain have left health authorities without licensed prevention tools.

Containment efforts are further complicated by conflicts, difficult transport routes, attacks on healthcare facilities, and gaps in contact tracing. While diagnosing infections has improved, the speed of response remains a critical bottleneck. Meanwhile, the newly launched Tumaini study in the DRC is testing different vaccine candidates, including Ervebo and a Moderna mRNA vaccine, aiming to provide reliable data on their efficacy against the Bundibugyo virus.

Why it matters This ongoing outbreak highlights the global challenge of translating scientific knowledge into rapid, practical medical countermeasures during health emergencies. Understanding vaccine efficacy gaps and logistical hurdles impacts public health responses and international preparedness efforts worldwide.