The World Health Organisation (WHO) has issued new emergency guidance restricting the use of the licensed Ervebo vaccine against Bundibugyo virus disease, saying it should currently be administered only under approved research protocols.
The decision followed an extraordinary meeting of the WHO’s Strategic Advisory Group of Experts on Immunisation (SAGE) held on August 19, 2026, as health authorities respond to the ongoing Bundibugyo outbreak.
In a statement issued on Tuesday, the global health agency said Ervebo should not presently be deployed through broad routine outbreak vaccination campaigns against Bundibugyo virus. Instead, its use should be incorporated into research designed to establish whether the vaccine is effective against the disease.
The WHO said a ring vaccination randomised controlled trial would provide the strongest evidence of Ervebo’s efficacy among populations affected by Bundibugyo virus disease.
Under a ring vaccination approach, people who have been exposed to an infected individual, as well as relevant contacts and frontline populations, can be vaccinated and monitored. The WHO said a randomised controlled trial using this strategy would offer the most robust way to determine whether Ervebo provides protection against Bundibugyo virus.
The organisation warned, however, that broader use of the vaccine before clinical trial evidence becomes available would require a comprehensive risk-mitigation strategy.
Such a plan, it said, would need to address potential risks associated with administering the vaccine during an outbreak while ensuring recipients’ health outcomes are monitored promptly and systematically.
The WHO stressed that its position on Ervebo does not change its existing recommendation for preventive vaccination against Ebola virus.
“WHO continues recommending preventive Ervebo vaccination for healthcare and frontline workers in Ebola virus priority areas with previous Ebola disease outbreaks,” the organisation said.
The agency specifically addressed the situation in areas affected by the current Bundibugyo outbreak, emphasising the need to generate reliable evidence before expanding the vaccine’s use.
“In areas affected by the current Bundibugyo outbreak, Ervebo should only support outbreak response through research protocols, including ring trials or observational vaccine-effectiveness studies.” WHO said, stressing evidence generation remains essential.
The WHO said such studies could help establish how well Ervebo performs against Bundibugyo virus under real-world outbreak conditions.
“Such studies could provide additional evidence about the potential performance of Ervebo against Bundibugyo virus during ongoing outbreaks,” it added.
According to the organisation, evidence generated through the studies could subsequently inform future vaccination policies and recommendations.
The WHO acknowledged that exceptional circumstances could arise in which conducting research is not feasible. In such cases, it said off-label use of Ervebo might be considered, provided systems are in place to maintain reliable vaccination records and monitor recipients’ health outcomes over time.
The agency also called for the accelerated development and rigorous evaluation of vaccines specifically designed to prevent Bundibugyo virus disease. It urged researchers and health authorities to advance work on post-exposure prophylaxis products and other medical countermeasures needed to strengthen preparedness and protect populations affected by outbreaks.
The organisation further appealed for closer coordination among partners supporting the Democratic Republic of Congo and other countries that may consider using Ervebo under research protocols.
It said stronger coordination would be necessary to ensure that research activities are implemented consistently and that emerging evidence is shared promptly among countries and response partners.
The WHO recommended the development and dissemination of master protocols for ring vaccination trials and high-quality observational studies. Such standardised research frameworks, it said, would help countries generate evidence more quickly and in a coordinated manner during the current outbreak and future public-health emergencies.
The latest guidance underscores the distinction between Ervebo’s established role in preventing Ebola virus disease and the still-unresolved question of its effectiveness against Bundibugyo virus. Until stronger evidence is available, the WHO is prioritising controlled research and systematic monitoring over widespread vaccination deployment against the virus.