Moderna's melanoma data just cost short sellers $5 billion in a day

Moderna's shares gained as much as 177% on Wednesday after a late-stage trial showed its personalised mRNA vaccine, paired with Merck's Keytruda, cut melanoma recurrence in Phase 3 patients. Short sellers, who held roughly 13.5% of the free float going into the print, took a mark-to-market hit of around $5 billion in a single session, according to data from S3 Partners cited by Bloomberg. Add prior 2026 losses and shorts are down close to $7.7 billion year to date. Moderna is still losing money, with analysts pencilling in a full-year loss near $6.20 a share, and Bank of America's response was to move from underperform to neutral, not to a buy. That gap between the stock price and the rating is the real disagreement here, over whether this is proof mRNA works against cancer or a trial away from being priced for a certainty it hasn't earned.