Health

Moderna shares fall after leaked cancer vaccine data despite positive trial results

Full results showed a 42% reduction in recurrence or death in some melanoma patients; analysts differ on the stock drop.

Updated Oct 23, 2026 · 00:14 UTC4 reports

The short version

Moderna shares fell as much as 25% Thursday after partial data on its Merck-developed cancer vaccine leaked.[CNBC]
The personalized vaccine intismeran autogene, paired with Merck's Keytruda, reduced recurrence or death by 42% in certain melanoma patients versus Keytruda alone.[CNBC]
BMO Capital Markets analyst Evan Seigerman called the relative reduction clinically meaningful, while UBS suggested expectations drove the stock reaction more than data.[CNBC]
Moderna shares later dropped 18% after the full results were made public, though they remained far above late-August levels.[Associated Press]

Moderna shares dropped as much as 25% Thursday after partial data on its cancer vaccine leaked.[CNBC]
Moderna shares dropped 18% Thursday after the full study results were made public.[Associated Press]
Intismeran autogene paired with Keytruda reduced recurrence or death by 42% versus Keytruda alone in certain melanoma patients.[CNBC]
BMO Capital Markets analyst Evan Seigerman called the relative reduction in recurrence or death clinically meaningful.[CNBC]
UBS analysts said the stock reaction may reflect massive expectations more than disappointing data.[CNBC]

The 42% figure is a relative reduction, and analysts disagree on whether the stock drop reflects weak data or inflated expectations.[CNBC]

Outlet counts describe coverage, not independent confirmation. Reports may share a wire service or original source.