WHO experts recommend trial of Ervebo vaccine against rare Ebola strain in DR Congo

The World Health Organization's vaccine experts have recommended a full-scale human trial for the Ervebo vaccine, the only approved Ebola vaccine, to assess its potential cross-protection against a rare strain of the virus spreading in the Democratic Republic of Congo. This recommendation comes as the number of confirmed cases in the ongoing outbreak surpasses 4,000, with nearly 2,000 fatalities.

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The members recommended Ervebo, the only licensed Ebola vaccine, be prioritized for inclusion in a randomized clinical trial in the context of the ongoing outbreak.

While Ervebo has proven effective against the more common Zaire strain of Ebola, early data, including animal trials, indicate it might offer some protection against the Bundibugyo strain currently circulating. Studies on non-human primates showed a significant survival rate among those vaccinated with Ervebo when exposed to the Bundibugyo strain, and a separate ferret study demonstrated 100% protection.

The proposed trial will be a "ring trial" in the DRC, focusing on vaccinating individuals who have come into contact with known cases. WHO chief Tedros Adhanom Ghebreyesus described the findings as "good news," though he cautioned that expectations should be managed regarding the vaccine's efficacy against symptomatic disease and transmission. Protection against a fatal outcome, however, may be achievable.

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Expectations need to be managed about its likely protective effect if used in a Phase III ring vaccination trial as efficacy against symptomatic disease and transmission may not be high, whereas protection against a fatal outcome may be achieved.

Despite the potential of Ervebo, experts emphasize that a specific vaccine for the Bundibugyo strain remains the preferred long-term solution. Two such vaccines are currently in early-stage human trials, with a third in development. Ebola is a severe hemorrhagic fever transmitted through bodily fluids, with the current outbreak concentrated in the northeastern Ituri province.

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Good news.