Moderna Stock Falls 25% on Melanoma Vaccine Phase 3 Data

Moderna shares fell 25.2% to $183.88 on October 22, 2026, the stock's steepest one-day percentage fall, per Reuters, erasing about $24 billion in market value. The drop followed Merck and Moderna's Phase 3 (large, late-stage trial) melanoma vaccine data. Topline, or headline, success was announced August 19; full results are slated for ESMO 2026, a major oncology conference.