Two new Ebola vaccine candidates are to join an ongoing clinical trial in the Democratic Republic of the Congo (DRC), the World Health Organization (WHO) announced on 5 November, as the country battles what has become the largest Bundibugyo virus outbreak in its history. The move follows a recommendation by WHO's independent Technical Advisory Group on Candidate Vaccines Prioritization and will mark the first time that vaccines specifically designed for the Bundibugyo species have been evaluated during an active outbreak of the disease.

The two candidates are ChAdOx1, developed by the University of Oxford in partnership with the Serum Institute of India, and mRNA-1469, developed by the American pharmaceutical and biotech company Moderna. WHO convened the expert group that this week recommended both candidates for further clinical evaluation based on available evidence. Their entry into the trial remains subject to national approvals.

As of 1 November, the DRC outbreak had produced more than 10,500 confirmed cases and 5,126 deaths, with the country having been battling the Bundibugyo strain for nearly six months. The epicentre remains Ituri province in the country's east, centred on Bunia, the provincial capital.

The two candidates will join WHO's Tumaini multi-vaccine trial — named after the Swahili word for "hope" — which was launched on 23 October in Bunia. The trial uses a ring-vaccination approach targeting contacts of confirmed Bundibugyo cases. WHO and partners pioneered that strategy during the West Africa Ebola outbreak a decade ago, when a trial in Guinea established the efficacy of the Ervebo vaccine. Ervebo, which was developed to treat the Zaire species of Ebola, is already being tested within Tumaini to determine whether it is also effective against the Bundibugyo species. Four vaccination rings have been set up, with more being prepared, and research into other potential treatments is also under way.

WHO Director-General Tedros Adhanom Ghebreyesus said the readiness of the new vaccines for clinical trials was "a testament to the power of science and partnership." He stressed, however, that vaccines alone will not end the outbreak but "could become a powerful new tool for bringing it under control."

This article is based on a primary source and has undergone editorial review prior to publication.