Inmazeb

Inmazeb is a triple monoclonal antibody cocktail developed by Regeneron Pharmaceuticals, approved by the FDA in October 2020 under the trade name Inmazeb. Its three components are atoltivimab, maftivimab and odesivimab-ebgn (REGN3470, REGN3479 and REGN3478 respectively). The cocktail targets the glycoprotein of Zaire ebolavirus — the viral surface protein that enables cell entry — neutralising the virus before it can infect host cells.

Inmazeb was evaluated in the PALM randomised clinical trial conducted during the 2018-20 DRC Kivu Ebola outbreak, which was among the largest controlled Ebola treatment trials in history. In that trial, Inmazeb demonstrated a CFR of approximately 34 per cent compared to approximately 49 per cent for ZMapp (the predecessor experimental cocktail) and 33 per cent for Ebanga, outperforming ZMapp and becoming one of two monoclonals recommended by the WHO as preferred therapies for Zaire ebolavirus disease. The drug mechanism relies on three antibodies binding distinct epitopes on the Zaire ebolavirus glycoprotein; using three antibodies simultaneously reduces the probability of viral escape mutations.

Regenerative capacity means Inmazeb can, in principle, be manufactured at scale, and Regeneron maintains emergency supply agreements that enabled rapid deployment to the 2018 DRC response. The US government Strategic National Stockpile holds Inmazeb as a Category A biological threat countermeasure.

Inmazeb cannot be used in the 2026 Bundibugyo Ebola outbreak because its FDA approval and clinical-efficacy data are specific to Zaire ebolavirus. The glycoprotein targeted by atoltivimab, maftivimab and odesivimab differs significantly between Zaire and Bundibugyo species, meaning the antibodies do not bind effectively to Bundibugyo's viral surface. There is no licensed Bundibugyo efficacy in Inmazeb's approval package.

One component of Inmazeb — REGN3479 (maftivimab) — targets a conserved region of the Filovirus fusion loop and has shown preclinical cross-neutralisation of Zaire, Bundibugyo and Sudan viruses in laboratory studies. This is a scientific signal of potential, not an approved therapy: the full Inmazeb cocktail's clinical-efficacy data is established for Zaire only, and REGN3479 alone is not an approved standalone therapeutic. Compassionate-use deployment of a single component, outside approved labelling, would require a specific regulatory pathway and manufacturer decision.

The WHO WATCH FOR section of the 17 May briefing explicitly flags whether Regeneron publishes cross-reactivity data for Inmazeb or Ebanga against Bundibugyo — data that does not currently exist in the public domain. Until such data exists, clinicians in Bunia and Mongbwalu cannot legally or ethically administer Inmazeb to Bundibugyo patients under standard care protocols.