Shares of Biogen (BIIB) fell 8.2% following the presentation of phase II CELIA study data on its Alzheimer’s drug, diranersen, at the Alzheimer’s Association International Conference (AAIC). The study did not meet its primary endpoint—the dose-response for cognitive decline at week 76 measured by the Clinical Dementia Rating–Sum of Boxes (CDR-SB).
Despite meaningful reductions in cognitive decline at the 60 mg dose—26% slowing in CDR-SB, 42% on ADAS-Cog13, and 50% on MMSE—the data indicated that higher doses did not yield greater benefits. Biogen confirmed that these results do not change the previous announcement from May 2026, when CELIA was reported to have failed in demonstrating expected dose-dependent efficacy.
Biogen, in collaboration with Ionis Pharmaceuticals (IONS), has yet to announce a timeline for the late-stage development of diranersen, which aims to provide an alternative to existing amyloid-targeting Alzheimer’s treatments.
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