On July 14, Biogen declined 7.06% in regular trading, falling to $194.18/share with turnover of approximately $149 million, after presenting full Phase 2 CELIA data for its investigational Alzheimer's drug Diranersen at the Alzheimer's Association International Conference.

Although Diranersen demonstrated robust Tau protein reduction and cognitive benefit across all studied doses at 18 months — with the 60 mg dose showing the strongest efficacy — the study confirmed it did not meet its primary endpoint, as the CDR-SB dose-response assessment was not satisfied. Despite Biogen announcing plans to advance Diranersen into Phase 3 registrational development, the market remains skeptical about the regulatory pathway given the missed primary endpoint. Morgan Stanley previously modeled a 30% probability of success, estimating Diranersen would contribute approximately 10% of the company's total revenue by 2035 at projected worldwide sales of $3.7 billion.

Notably, earlier in the session Biogen had risen over 5% on news of FDA approval of the Leqembi subcutaneous injection formulation, but those gains were fully reversed following the CELIA data presentation.

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