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Regeneron
OrganisationUS

Regeneron

US biotech that developed Inmazeb, the Zaire ebolavirus monoclonal cocktail with no approved Bundibugyo efficacy.

Last refreshed: 17 May 2026 · Appears in 1 active topic

Key Question

Could Regeneron's Inmazeb work against Bundibugyo, and will the company publish that data?

Timeline for Regeneron

#712 Jun

Developed REGN3479 monoclonal antibody now in the Bundibugyo treatment trial

Pandemics and Biosecurity: First Ebola treatment trial goes live
#317 May

No vaccine, no treatment, no MCM

Pandemics and Biosecurity
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Common Questions
Does Regeneron's Ebola drug work against the current outbreak strain?
No. Regeneron's Inmazeb (REGN-EB3) is FDA-approved for Zaire ebolavirus only. The current Ituri outbreak is Bundibugyo ebolavirus, a distinct species. Regeneron's REGN3479 component shows preclinical cross-neutralisation activity against Bundibugyo, but this has not been tested in clinical trials and no cross-reactivity data has been published for the Inmazeb cocktail against Bundibugyo.Source: FDA label; PubMed Central PMC10032372
What is Inmazeb and how does it work against Ebola?
Inmazeb is a triple monoclonal antibody cocktail (atoltivimab, maftivimab, odesivimab) developed by Regeneron. It targets the glycoprotein of Zaire ebolavirus, blocking the virus's ability to enter host cells. It was approved by the FDA in October 2020 after the PALM trial in DRC showed it significantly reduced mortality compared to ZMapp. It does not have demonstrated efficacy against Bundibugyo or Sudan species.Source: FDA; PALM trial NEJM 2019
Why won't Regeneron's Ebola treatment work in the Ituri outbreak?
Ebola monoclonal therapies are species-specific because they target the viral glycoprotein, which differs between Zaire, Bundibugyo, Sudan, Reston, Tai Forest and Bombali. Inmazeb was designed and trialled against Zaire ebolavirus, which has the largest outbreak history. Bundibugyo's glycoprotein is structurally different enough that there is no licensed cross-species efficacy.Source: WHO R&D Blueprint; PubMed Central PMC10032372

Background

Regeneron Pharmaceuticals is a US biotechnology company headquartered in Tarrytown, New York, founded in 1988. It developed Inmazeb (atoltivimab/maftivimab/odesivimab, also designated REGN-EB3), a triple monoclonal antibody cocktail that became one of two FDA-approved treatments for Ebola virus disease in October 2020 following the PALM (Pamoja Tulinde Maisha) randomised controlled trial conducted in DRC during the 2018-19 Kivu outbreak. Inmazeb targets the glycoprotein of Zaire ebolavirus specifically.

Regenerons REGN3479 monoclonal component shows preclinical cross-neutralisation activity against Bundibugyo and Sudan ebolaviruses in addition to Zaire, but it is not approved as a standalone therapeutic. The full Inmazeb cocktail has not been evaluated in clinical trials against non-Zaire species. As of the 17 May 2026 PHEIC declaration, no cross-reactivity data for Bundibugyo has been published by Regeneron. The WHO WATCH FOR list includes whether Regeneron publishes cross-reactivity data as one of the key developments to monitor in the coming weeks.

Regenerons position in this outbreak is as the developer of an important tool that does not apply: Inmazeb is highly effective against Zaire, the species behind the 2018 Kivu outbreak, but has no licensed indication for Bundibugyo. The commercial and regulatory pathway for any cross-species expansion would require either new clinical trial data or compassionate-use determination, and neither is publicly initiated as of the PHEIC date.

Source Material
Inmazeb — Regeneron