The allocation, announced by the World Health Organisation (WHO) and the Africa Centres for Disease Control and Prevention (Africa CDC), comes as the outbreak continues to spread across the country and record high levels of transmission place increasing pressure on health workers and communities.
The DRC government requested access to vaccines from the global Ebola virus disease stockpile managed by the International Coordinating Group on Vaccine Provision (ICG) last week. The ICG subsequently approved an immediate initial release of 70,000 doses.
Of the allocation, 20,000 doses will be used in a Phase III clinical trial, designed to determine whether Ervebo can provide protection against Bundibugyo virus. The remaining 50,000 doses will be offered to frontline and healthcare workers, following recommendations from WHO’s Strategic Advisory Group of Experts on Immunization (SAGE).
The decision to combine vaccination with clinical research reflects a major scientific challenge confronting the response: Ervebo is not specifically licensed for Bundibugyo virus disease.
Ervebo is a licensed and WHO-prequalified vaccine used to prevent Ebola disease caused by Zaire ebolavirus. WHO currently says there is insufficient evidence to establish that it protects people against Bundibugyo virus, which is a different species.
However, early laboratory and animal studies have raised the possibility that the vaccine could offer some degree of cross-protection. The Phase III study is therefore expected to provide critical evidence that could determine whether Ervebo has a role in responding to future Bundibugyo outbreaks.
A vaccine — and a scientific test
WHO's technical advisory group on candidate vaccine prioritisation recently recommended that Ervebo be prioritised for inclusion in a randomised clinical trial during the current DRC outbreak.
The recommendation followed a review of emerging laboratory, animal and other evidence concerning the vaccine's potential ability to protect against Bundibugyo virus. The advisory group said Ervebo could proceed directly to a Phase III research study in the absence of a Bundibugyo-specific vaccine ready for evaluation.
The approach means the vaccine allocation will serve two purposes: protecting people at particularly high risk of exposure while generating evidence that could help guide future outbreak policy.
WHO stressed that anyone offered Ervebo — whether through the clinical trial or outside it — must be informed about the potential risks, possible benefits and limitations of using the vaccine against Bundibugyo virus. Participants must also provide informed consent.
Outbreak reaches unprecedented scale
The vaccination effort comes as the DRC confronts what WHO describes as the largest Ebola outbreak ever reported in the country.
As of 12 August, the DRC had recorded 4,665 confirmed cases and 2,184 deaths, representing a crude case-fatality ratio of 46.8 per cent. The outbreak had expanded from the Mongbwalu health zone in Ituri Province to 54 health zones across six provinces — Ituri, North Kivu, South Kivu, Haut-Uélé, Tshopo and Bas-Uélé.
WHO has described the outbreak as being in a phase of intense transmission, with the number of cases and affected areas continuing to rise. During the week of 3 to 9 August, the country recorded its highest weekly totals, with 579 confirmed cases and 304 deaths reported.
The scale of the epidemic has already surpassed the previous record Ebola outbreak in the DRC, which recorded 3,317 cases between 2018 and 2020.
Ituri remains the epicentre, accounting for the overwhelming majority of cases and deaths. WHO reported that at least 155 healthcare workers had been infected by 9 August, including 45 deaths, underscoring the occupational risks facing medical teams working to contain the disease.
Movement and insecurity complicate response
The outbreak has been particularly difficult to contain because of population movement, insecurity, limited healthcare capacity and cross-border travel.
WHO's latest assessment said the outbreak had expanded rapidly since it was detected in May, while transmission chains remained unidentified in many areas. The agency rated the risk as very high within the DRC and high for neighbouring countries, particularly those sharing land borders with the country.
Cross-border movement has already resulted in infections outside the DRC, although sustained transmission has not been reported beyond the country. Uganda, France and Germany have recorded imported cases linked to the outbreak.
WHO and Africa CDC have consequently called for a stronger community-led response, including earlier detection, improved contact tracing, faster access to care and greater support for frontline health workers.
The agencies have also stressed that communities must play a central role in the response if transmission is to be brought under control.
Search for a Bundibugyo-specific vaccine
While Ervebo is being evaluated, researchers are also working on vaccines specifically designed to target Bundibugyo virus.
Unlike Ervebo, which was developed against Zaire ebolavirus, candidate vaccines aimed specifically at Bundibugyo virus are intended to address the biological differences between Ebola species.
WHO currently states that there are no licensed vaccines specifically for Bundibugyo virus disease, although several candidates are under development.
The development of a targeted vaccine is therefore regarded as an important long-term priority, particularly given the severity and scale of the current outbreak.
The immediate response is also being supported by research into treatments. WHO said a clinical trial investigating potential treatments for Bundibugyo virus disease began enrolment in July and has been operating at clinical facilities in Ituri.
Nigeria strengthens preparedness
The worsening situation in the DRC has also prompted heightened preparedness across the region, including in Nigeria.
The Nigeria Centre for Disease Control and Prevention (NCDC) previously assessed the overall risk of importation as high, citing regional transmission, international travel, population movement, major airports and seaports, porous land borders and trade routes.
The agency identified 10 states and the Federal Capital Territory as high-risk areas in its May preparedness advisory: Lagos, the FCT, Rivers, Kano, Enugu, Borno, Akwa Ibom, Cross River, Taraba and Adamawa. It placed a further 12 states in a moderate-risk category.
NCDC called on states to strengthen surveillance, isolation and referral arrangements, infection prevention and control measures, and their ability to identify and respond rapidly to suspected cases.
Nigeria has no confirmed case linked to the current outbreak according to the NCDC advisory, but authorities have emphasised that preparedness must begin before an imported case is detected.
A critical test for Ebola preparedness
For the DRC, the arrival of the 70,000 doses represents both an immediate public-health intervention and an important scientific opportunity.
The 50,000 doses earmarked for frontline and health workers could provide an additional layer of protection for personnel working in high-risk environments, while the 20,000-dose clinical trial could answer a question that has remained unresolved since the Bundibugyo outbreak began: whether a vaccine developed for another Ebola species can meaningfully protect humans against this virus.
WHO and Africa CDC have pledged continued support for the DRC government as it works to contain transmission, protect affected communities and generate scientific evidence that could strengthen preparedness for future outbreaks.
The challenge, however, remains immense. With transmission expanding, mortality still high and healthcare workers continuing to become infected, authorities face a race against time to combine vaccination, surveillance, treatment, community engagement and cross-border preparedness before the outbreak spreads further.