Moderna Stock Plummets After Positive Cancer Vaccine Data Leaks Online
Moderna shares dropped seventeen percent Thursday after Phase 3 trial results for its melanoma cancer vaccine leaked to social media two days early. The personalized vaccine, called intismeran autogene, developed with Merck, reduced the risk of cancer recurrence or death by forty-two percent when combined with the drug Keytruda, compared to Keytruda alone. The data met the trial's primary endpoints and showed eighty-two percent of patients receiving the combination remained alive and cancer-free at two years, versus seventy percent on Keytruda alone. Despite these positive results, investors sold off the stock heavily, wiping roughly twenty-four billion dollars from the company's market value at its intraday low. Analysts attributed the decline to sky-high expectations built into Moderna's massive year-to-date rally of over five hundred percent, rather than disappointment with the vaccine itself.
Key facts
- Moderna stock fell as much as 25% intraday and closed down 17.6% at $202.63 on October 22, 2026
- Intismeran autogene combined with Keytruda reduced melanoma recurrence or death risk by 42% versus Keytruda alone in 1,137 patients
- Two-year disease-free survival was 82.2% with combination treatment versus 70% with Keytruda alone
- Trial data leaked from medical news site Oncology Central around 12:30 p.m. ET, two days before scheduled ESMO Congress presentation
- Moderna shares had risen 733% from December 2025 close of $29.49 to $245.81 before the leak
- European Society for Medical Oncology (ESMO) launched investigation into embargo breach and subsequently lifted embargo on full dataset
Limits of this briefing
Most coverage comes from financial and business outlets rather than explicitly partisan news sources. Left and right-leaning media outlets showed minimal coverage of this specific story as of October 23, 2026. Some reporting on the leak mechanism conflates the financial reaction with the clinical validity of the data, which some observers distinguish carefully.
Sources
- CNBC: Moderna shares plunge after cancer vaccine data leaks — despite positive results Centre
- Bloomberg: Moderna, Merck Shares Drop After Reports of Melanoma Vaccine Data Leak Centre
- CNN: Experimental mRNA vaccine cuts risk that melanoma returns by 42% Centre
- Yahoo Finance: Moderna Stock Plunges as Apparent Leak Reveals Phase 3 Melanoma Vaccine Data Centre
- Scientific American: Here's what the new Merck-Moderna mRNA cancer vaccine data actually show Centre