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Moderna stock falls 17% as cancer vaccine results disappoint high hopes

Moderna shares closed down 17.4% on Thursday after Merck and Moderna released detailed Phase 3 results showing their personalized melanoma vaccine cut the risk of recurrence or death by 42%. Analysts called it a sell-the-news reaction after a months-long rally.

By US Brief desk · Updated 2026-10-22T15:18:00-07:00

AI-assisted · US Brief desk · Sources listed below

A street in Cambridge, Massachusetts, with a white office building bearing the red Moderna logo in the background, framed by autumn trees

What happened

Moderna shares closed at $203.07 on Thursday, down $42.74 or 17.39%, according to StockAnalysis, after falling as much as 26% during the session. Merck and Moderna released detailed results from the Phase 3 trial of their personalized melanoma vaccine after the figures briefly appeared early on an oncology website, Reuters reported. Merck, Moderna's partner on the vaccine, fell nearly 1%.

Why it matters

Melanoma is the deadliest common skin cancer, and this would be the first personalized mRNA cancer treatment to succeed in a Phase 3 trial, according to the companies' August release. They said they plan to share the data with regulators, a step toward a possible FDA filing. For investors, Moderna's swing shows how much of its value now rides on this one product.

More context

What the results showed: Adding the vaccine, intismeran autogene, to Merck's immunotherapy Keytruda cut the risk of melanoma returning or death by 42% compared with Keytruda alone (hazard ratio 0.58), the companies said. It lowered the risk of distant spread or death by 38% (hazard ratio 0.62). After a median follow-up of 24.6 months in 1,137 patients whose melanoma had been surgically removed, 82.2% on the combination were alive and recurrence-free at two years, versus 70.0% on Keytruda alone. Overall survival data are still immature but show a favorable trend. The full results will be presented Saturday at the European Society for Medical Oncology (ESMO) congress and published in the New England Journal of Medicine. The vaccine is made for each patient from the mutations in their own tumor.

Why good numbers sank the stock: The shares had climbed to a 52-week high of $254.48 on Wednesday, more than 11 times their 52-week low of $22.28 last November, per CNBC's quote data. Analysts cited by Reuters described the drop as a sell-the-news reaction after a months-long rally built on high expectations.

By the numbers: 17.4%: Moderna's drop at the close. About $17.1 billion: the stock market value erased, by US Brief's math using CNBC's count of 399.24 million shares. 42%: the cut in the risk of recurrence or death. 1,137: patients in the trial.

Timeline: Aug. 19: Merck and Moderna said the trial met its main goal of recurrence-free survival and a key secondary goal, without releasing the size of the benefit; Moderna's shares jumped as much as 160% that day, Reuters reported. Oct. 21: Moderna hit its 52-week high. Oct. 22: detailed results briefly appeared online early, then the companies officially released them. Oct. 24: the scheduled ESMO presentation.

What's still unknown: Overall survival results are still being tracked, and the companies have not given a date for a regulatory filing. Full data are due at ESMO on Saturday.

5 listed sources

References listed by US Brief; a source count is not a verification score.

Editorial sourcing notes

Trial figures are from Merck and Moderna's Oct. 22 release. The stock close is from StockAnalysis. The market-value estimate is US Brief's math using CNBC's share count. Photos are file photos.

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