Celldex Falls 13% as Anaphylaxis Cases Shadow Positive Phase 3 Barzolvolimab Data

Celldex Therapeutics shares dropped 13% in early trading on September 22, 2026, after investors focused on two anaphylaxis cases in a barzolvolimab-dosed group despite positive Phase 3 results for the immune drug. The company reported that two late-stage trials of barzolvolimab in chronic spontaneous urticaria met their primary endpoint, with about half of treated patients achieving complete response at 24 weeks versus 15%-18% on placebo. CEO Anthony Marucci called the anaphylaxis incidence "extremely low" across roughly 2,400 patients treated. Cantor Fitzgerald forecast peak sales of $4.8 billion, while Stifel said it remains optimistic given anaphylaxis warnings on rival biologics such as Dupixent. Celldex plans to file for FDA approval in 2027 and is testing the drug in three other indications.