Ervebo

Ervebo (rVSV-ZEBOV-GP) is a recombinant vesicular stomatitis virus-vectored vaccine against Zaire ebolavirus, developed by Merck & Co and WHO-prequalified in November 2019. It received FDA approval in December 2019 and EMA approval in November 2019. The vaccine uses a live, attenuated vesicular stomatitis virus engineered to express the Zaire ebolavirus glycoprotein, triggering an immune response against Zaire Ebola specifically.

Ervebo was deployed in the 2018 DRC Equateur outbreak in a ring-vaccination strategy: contacts and contacts-of-contacts of confirmed cases were vaccinated to create an immune ring around the outbreak. Ring vaccination of 3,302 contacts contributed to controlling the Equateur outbreak at 54 cases and 33 deaths in approximately three months. In the larger 2018-20 Kivu/Ituri epidemic, Ervebo was deployed under a compassionate-use protocol before its formal prequalification, and data from that deployment contributed to the final WHO prequalification.

Ervebo is manufactured by Merck at limited global supply. WHO and GAVI maintain strategic stockpiles for rapid deployment. The vaccine's efficacy is highly species-specific because it generates immunity to the Zaire glycoprotein only — a glycoprotein that shares insufficient structural similarity with the Bundibugyo glycoprotein to confer cross-protection.

Ervebo cannot be used in the 2026 Bundibugyo Ebola outbreak. The WHO R&D Blueprint Filovirus roadmap, published in Q1 2026, explicitly named non-Zaire Ebola species — including Bundibugyo — as a research-priority gap. No vaccine has entered the clinical phase of evaluation specifically for Bundibugyo, meaning there is no experimental product even for compassionate-use ring vaccination.

The contrast with the 2018 Equateur response is operationally significant: Equateur was controlled with Ervebo ring vaccination of 3,302 contacts as the primary epidemiological intervention. In Ituri in 2026, there is no equivalent tool. Contact-tracing teams cannot offer vaccinated contacts the protection that ring vaccination provided in 2018; healthcare workers entering Ebola treatment units in Bunia and Mongbwalu have no vaccine protection. Maria Van Kerkhove of WHO acknowledged the gap explicitly: the agency stood ready to deploy vaccines "should it turn out to be a strain where a vaccine can be used" — a conditional that Bundibugyo does not satisfy.

The absence of Ervebo cross-protection also means healthcare worker deaths are more likely in 2026 than in 2018: ring vaccination protected health workers in Equateur; no such protection exists for Ituri health workers. Four healthcare worker deaths in clinically suggestive contexts have been confirmed in the WHO PHEIC technical assessment.