Stock Market Today, Oct. 22: Moderna Stock Plummets 18% on Melanoma Vaccine Data Leak Reports

Moderna's stock fell 18% after reports of a data leak regarding its personalized melanoma vaccine showed a 42% reduction in recurrence or death risk when paired with Merck's Keytruda—lower than Phase II results of 49%. The full Phase 3 results were scheduled for release on October 24, and the leaked figures fell short of market expectations despite the company's 600% gain in 2026.