Why Is Moderna (MRNA) Stock Price Up 176.97% Today, August 19? Phase 3 Cancer Vaccine Success with Merck Drives Historic Surge

Moderna surged after its personalized mRNA cancer vaccine with Merck met Phase 3 melanoma endpoints versus KEYTRUDA alone, marking a rare clinical validation for individualized neoantigen therapy and supporting a platform re-rating beyond COVID revenues. The move was amplified by short covering (reported multi-billion short losses), increasing volatility and leaving a wide post-gap trading range. Near-term focus shifts to full data disclosure, safety/durability, and regulatory filing discussions.