Moderna and Merck Announce Positive Phase 3 Trial Results for Personalized mRNA Cancer Vaccine
On August 19, 2026, Moderna (NASDAQ:MRNA) and Merck & Co. (NYSE:MRK) announced that their personalized mRNA cancer vaccine combined with Keytruda met its primary endpoints in a Phase 3 trial for melanoma. The results marked the first successful late-stage trial of a personalized cancer vaccine, leading to an immediate surge in Moderna's stock by as much as 177% and Merck’s shares rising over 12%. This milestone is significant given Moderna's declining revenue from its earlier mRNA-based vaccines like those for COVID-19. The combination therapy showed statistically significant improvements in reducing cancer recurrence or death risk, with a reported 49% reduction compared to Keytruda alone. Merck’s drug remains the standard of care for melanoma and is now validated as an effective partner in this new treatment approach. However, neither company has released full numerical data yet, raising questions about whether market enthusiasm outpaces available evidence. Despite these positive results, Moderna's stock still trades at less than a third of its 2021 peak and remains the most shorted stock in the S&P 500. Analysts remain divided on how much this trial will translate into broader success for other cancers or long-term financial gains.
Topics: biotech cancer_treatment mRNA_vaccine stock_movement