WHO director-general Tedros Adhanom Ghebreyesus said in a social media post on Friday that participants in the trial had been vaccinated with Ervebo, a vaccine approved for the more common Zaire strain of Ebola. The full-scale human trial will test whether Ervebo offers any cross-protection against the Bundibugyo species that is behind the current epidemic.
"This trial will help us understand whether any of the vaccine candidates designed for Bundibugyo virus work," Tedros wrote on X. "WHO is supporting this DRC-led effort to find answers and save lives."
The DRC declared its 17th and worst-ever Ebola outbreak in May and has since reported more than 9,700 cases, with deaths exceeding 4,600. The WHO responded by triggering a public health emergency of international concern, its second-highest alert level. The outbreak has now been reported in four countries across eastern, central and western Africa, the widest geographic spread of any Ebola outbreak on the continent to date.
The trial, known as Tumaini, is a single framework able to test the safety, efficacy and immunogenicity of multiple vaccines. It uses a ring vaccination approach, immunising contacts deemed to be at high risk of infection. Two Bundibugyo-specific candidate vaccines are expected to enter the trial shortly: a ChAdOx1 adenoviral vector jab being developed by the University of Oxford, and an mRNA vaccine from the US-based Moderna group. Both have received funding from the Coalition for Epidemic Preparedness Innovations (CEPI).
The trial will also include pregnant women and children aged 12 and over, generating evidence for populations often excluded from clinical trials. WHO emergencies director Chikwe Ihekweazu said the trial was set up to generate the rigorous evidence needed to determine whether the participating vaccines could protect people at risk.