Moderna's cancer vaccine stock rocketed 177% then crashed 25% the next day — and RFK Jr had axed $500M in mRNA funding a year earlier. Who read this right?
On August 19, 2026, Merck and Moderna announced that their personalized mRNA cancer vaccine "intismeran," paired with Merck's Keytruda, showed a "clinically meaningful improvement" over Keytruda alone in a Phase 3 trial for high-risk melanoma patients after surgery — the first-ever randomized late-stage trial to test this approach. Moderna's stock exploded 177% that day, its best day ever, briefly valuing the company near $70 billion, while Merck shares also jumped. The catch: the companies didn't release the actual numbers, saying full data would come at a future medical conference. The next day, Moderna stock plunged 25%, wiping out about $18 billion in value, which analysts mostly blamed on profit-taking rather than doubt about the science (one Bank of America analyst still quadrupled his price target to $170). This all lands a year after HHS Secretary Robert F. Kennedy Jr. cancelled nearly $500 million across 22 mRNA vaccine development projects in August 2025, arguing mRNA "fails to protect effectively" against illnesses like COVID and flu — cuts that mostly hit respiratory-vaccine work, not this cancer program, but that fueled broader skepticism about the entire mRNA platform. Moderna's president said he hopes this week's results help move mRNA past being "pigeonholed" as just pandemic vaccine tech.
