Ebola in DRC: Exploring Off-Label Vaccine Use Amidst Conflict

The Democratic Republic of the Congo is facing its fourth-largest Ebola outbreak on record, confirmed just last week. The virus—Bundibugyo ebolavirus—is spreading in a volatile conflict zone, making containment a major challenge. Unlike previous outbreaks of the Zaire species, there is no approved vaccine for this strain. However, a sliver of scientific evidence suggests that Merck’s Ervebo, licensed for Zaire ebolavirus, might still offer partial protection. Here, we break down the situation and the experts' dilemma.

What makes the current Ebola outbreak in DRC especially dangerous?

The outbreak, caused by the Bundibugyo species of Ebola, is already the fourth largest ever recorded. It emerged in a region of the Democratic Republic of the Congo that has been plagued by ongoing conflict and insecurity. This makes it incredibly difficult for health workers to track cases, trace contacts, and safely bury the dead—all critical steps for containing the virus. Previous experience with Ebola in conflict zones has shown that containment becomes a major challenge when communities are inaccessible or distrustful of authorities. The situation is further complicated by the lack of a specifically approved vaccine for the Bundibugyo strain, limiting the standard preventive tools available.

Why is there no approved vaccine for the Bundibugyo ebolavirus?

Vaccine development typically targets the most common or historically deadliest strains. For Ebola, all licensed vaccines—such as Merck's Ervebo—were designed and tested against the Zaire ebolavirus, which caused the catastrophic 2014-2016 West Africa outbreak. The Bundibugyo species is rarer and less studied; it was first identified in 2007. As a result, no vaccine has undergone the rigorous clinical trials needed for approval specifically against this strain. The research pipeline for rare viruses is slower, and manufacturers often prioritize strains with the highest global health impact.

Could the existing Ervebo vaccine work against Bundibugyo?

Experts are cautiously optimistic but admit the evidence is limited. Ervebo is designed to target the Zaire ebolavirus, but early laboratory studies suggest that antibodies generated by the vaccine may also cross-react with the Bundibugyo virus. This is because the two species share some structural similarities in their surface proteins. However, these findings come from small-scale experiments, not large human trials. In the absence of a specific vaccine, some scientists argue that using Ervebo off-label is a long shot—but one worth trying given the grim alternative. The World Health Organization and DRC health authorities are weighing this gamble carefully.

What containment challenges does the conflict zone create?

The outbreak is unfolding in an area with active armed groups and limited infrastructure. Health workers have been attacked in the past, and distrust of outsiders runs deep. This makes it difficult to rapidly isolate patients, conduct safe burials, and vaccinate contacts. In previous outbreaks in similar settings, the virus has spread undetected for weeks before being identified. The conflict also disrupts supply chains for protective equipment and diagnostics. Without a stable security environment, response teams cannot implement the ring vaccination strategy that proved successful against Zaire ebola, further complicating control efforts.

How does this outbreak compare to previous Ebola outbreaks?

This is the fourth largest Ebola outbreak on record, in terms of case numbers. The largest were the 2014-2016 West Africa epidemic (Zaire species, over 28,000 cases), the 2018-2020 DRC outbreak (Zaire, ~3,500 cases), and a 2000 Uganda outbreak (Sudan species). While the current case count is relatively small, the rate of increase and the challenging setting make it alarming. Unlike past outbreaks of Bundibugyo (e.g., Uganda 2007, DRC 2012), this one is occurring in an active conflict zone, which could allow the virus to spread farther before being contained.

What are experts recommending as a response?

Leading health officials are considering deploying Merck’s Ervebo as an off-label, experimental measure. This would involve emergency use authorization and robust informed consent. The decision hinges on whether the theoretical benefit outweighs the risks and logistical hurdles. Some experts advocate for testing the vaccine in a small clinical trial to gather more data, while others argue that in a humanitarian crisis, any potential protection is better than none. At the same time, containment measures like surveillance, contact tracing, and community engagement are being ramped up—but all depend on a fragile peace.