Ervebo
Merck's rVSV-ZEBOV Ebola vaccine; WHO-prequalified 2019 for Zaire only; no cross-protection against Bundibugyo.
CEPI-funded developers built a Bundibugyo vaccine candidate on Ervebo's own rVSV platform, and on 31 July 2026 Hilleman Laboratories put the first Bundibugyo-matched shot into trial production, nine years after Ervebo itself won approval for Zaire ebolavirus alone.
Last refreshed: 31 July 2026 · Appears in 1 active topic
If the Ervebo vaccine crushed the 2018 Ebola outbreak, why can't it be used in 2026?
Timeline for Ervebo
Mentioned in: CEPI puts a Bundibugyo vaccine in trials
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Pandemics and BiosecurityLicensed Ebola vaccine targeting only the Zaire species, not Bundibugyo
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Ervebo (rVSV-ZEBOV-GP) is a recombinant vesicular stomatitis virus vaccine against Zaire ebolavirus, developed by Merck and WHO-prequalified in November 2019 after FDA and EMA approval that same year. It uses a live, attenuated vesicular stomatitis virus engineered to express the Zaire glycoprotein, triggering immunity against that species specifically.
Its clearest result came in the 2018 DRC Equateur outbreak, where ring vaccination of 3,302 contacts helped hold the epidemic to 54 cases and 33 deaths in about three months; earlier compassionate use during the larger 2018-20 Kivu epidemic fed the data behind its formal prequalification. Merck manufactures at limited global supply, with WHO and GAVI holding strategic stockpiles for rapid deployment.
Because Ervebo's immunity targets the Zaire glycoprotein only, a protein structurally too different from Bundibugyo's for cross-protection, it cannot be used for ring vaccination or healthcare-worker protection in the 2026 Ituri outbreak. WHO's Maria Van Kerkhove has said the agency stands ready to deploy vaccines only where the strain allows it, a condition Bundibugyo does not meet.
Its own vaccine platform is being repurposed
CEPI has funded at least four rVSV-based Bundibugyo vaccine candidates since 1 June 2026, the same vector technology behind Ervebo's own rVSV-ZEBOV design, and by 9 June had committed $63.7 million across the portfolio. A CEPI-funded candidate from Hilleman Laboratories, also built on the rVSV platform, entered trial production on 31 July, the first Bundibugyo-matched vaccine of any kind.
None of these candidates has reached the ring-vaccination stage that made Ervebo decisive in the 2018 Equateur response, and none will be ready during the current outbreak; the platform's track record explains the funding choice, not its speed.