By Michael Omotosho |
The World Health Organization (WHO) has recommended that Ervebo, the only licensed vaccine against Ebola virus disease, be prioritised for a Phase 3 clinical trial during the ongoing Bundibugyo virus disease outbreak in the Democratic Republic of the Congo (DRC).
The recommendation follows new evidence from animal studies suggesting that Ervebo may offer some protection against Bundibugyo virus disease, particularly against death, although its ability to prevent symptomatic disease or transmission remains uncertain.
The WHO Technical Advisory Group on Candidate Vaccine Prioritization (TAG-CVP) made the recommendation after its third meeting on 31 July 2026, where it reviewed additional evidence on Ervebo’s potential cross-protection against Bundibugyo virus.
New animal studies strengthen evidence
According to the meeting report, new findings from ferret and non-human primate (NHP) studies strengthened earlier evidence that Ervebo could provide cross-protection against Bundibugyo virus.
In the ferret study, research-grade rVSV-EBOV, the vaccine platform used for Ervebo, provided 100 per cent protection to vaccinated ferrets challenged with Bundibugyo virus, whether given as a single dose or through a prime/boost schedule. All control animals died within 10 days of infection.
A separate NHP study also produced encouraging results. Three of four animals vaccinated with Ervebo survived a challenge with virulent Bundibugyo virus, compared with about 25 per cent of animals in the control group. The surviving vaccinated animals had lower clinical scores than the controls, although they developed viraemia.
The advisory group said the evidence from the animal studies suggests that Ervebo could protect against death, even though it may not provide complete protection against infection or symptomatic disease.
The report noted that NHP studies remain the primary indicator of potential Ebola vaccine efficacy, while the ferret findings provided additional supportive evidence. Across two NHP studies, six of eight vaccinated animals survived, representing a cumulative survival rate of 75 per cent.
WHO says no safety concerns
Safety was another key consideration in the recommendation.
The TAG-CVP unanimously agreed that there were no safety concerns about using Ervebo in a clinical research study. The vaccine is already licensed by regulatory agencies in North America, Europe and Africa and has been administered to hundreds of thousands of people in Africa.
The vaccine is also prequalified by WHO, with doses available through the WHO International Coordinating Group on Vaccine Provision stockpile.
However, WHO said expectations about the vaccine’s effectiveness should remain realistic.
The advisory group said Ervebo may have limited effectiveness against symptomatic disease and transmission, while protection against a fatal outcome may be more achievable.
BDBV-specific vaccine remains preferred
Despite the recommendation, WHO said a vaccine specifically designed against Bundibugyo virus remains the preferred option.
Several BDBV-specific vaccine candidates are currently under development, but none was considered ready for use in the current outbreak because pre-clinical testing was incomplete or Phase 1 clinical data were not yet available.
The TAG-CVP therefore considered Ervebo a practical option for immediate evaluation while work on BDBV-specific vaccines continues.
The group said Ervebo could proceed directly into a Phase 3 trial without an initial Phase 2 evaluation, given the extensive safety, reactogenicity and immunogenicity data already available for the vaccine.
Evidence still has limitations
WHO cautioned that the evidence supporting the recommendation is still developing.
Some of the studies reviewed by the advisory group were unpublished or had not undergone peer review, and several findings remain preliminary. The report also noted that some earlier studies used research-grade rVSV-EBOV rather than the licensed Ervebo product.
However, the advisory group said the findings were broadly consistent across studies, with evidence of low-level cross-reacting antibodies against Bundibugyo virus detected in people vaccinated with Ervebo.
With one exception, TAG-CVP members supported prioritising Ervebo for inclusion in a Phase 3 trial during the ongoing outbreak, particularly because no BDBV-specific vaccine is currently available for use.
The proposed trial is expected to generate evidence that could guide future decisions on whether Ervebo should be used more widely against Bundibugyo virus disease.
WHO’s technical advisory group is expected to continue reviewing new evidence as it becomes available and adjust its recommendations where necessary.
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