Moderna, Merck Shares Slide After Positive Cancer Data Leak

WHO:

Bloomberg Markets - Moderna and Merck are developing a personalized melanoma vaccine.

CNBC - The vaccine, intismeran autogene, was developed by Moderna with Merck and was tested with Merck’s immunotherapy Keytruda.

CNBC - Merck CEO Robert Davis discussed the vaccine’s manufacturing timeline with CNBC.

CNBC - BMO Capital Markets analyst Evan Seigerman said the recurrence-or-death reduction was clinically meaningful.

CNBC - UBS analysts described the results as “overall a strong data set.”

WHAT:

Bloomberg Markets - Moderna and Merck shares fell after data on their personalized melanoma vaccine failed to convince investors that a new era of cancer treatments had arrived.

CNBC - Moderna shares dropped as much as 25% after partial data on the cancer vaccine leaked.

CNBC - Full data released after the leak showed the vaccine plus Keytruda reduced the risk of melanoma recurrence or death by 42% compared with Keytruda alone.

CNBC - The combination reduced the risk of cancer spreading to distant parts of the body or death by 38% compared with Keytruda alone.

CNBC - At two years, about 82% of patients receiving the vaccine plus Keytruda were alive without melanoma returning, compared with 70% receiving Keytruda alone.

CNBC - The detailed phase 3 trial results were set to be presented at the European Society for Medical Oncology conference.

CNBC - Moderna shares had risen more than 530% year-to-date; Merck shares had climbed nearly 41%. Merck shares fell about 1%.

CNBC - Seigerman said, “Such a reaction likely reflects inflated expectations into the full data release, rather than a true indictment on the efficacy of the combo therapy.”

WHERE:

CNBC - The vaccine’s phase 3 results were scheduled for presentation at the European Society for Medical Oncology conference.

WHY:

Bloomberg Markets - Investors were not persuaded the data signaled a new era of cancer treatments.

CNBC - Analysts said the share-price reaction may reflect elevated or inflated expectations rather than disappointing data.

HOW:

CNBC - The treatment combines a personalized vaccine with Keytruda.

CNBC - Manufacturing the personalized vaccine can take six weeks; Davis said Merck believes it may shorten the process, potentially enabling faster, broader access.

(UPDATED October 22, 2026 22:14 UTC)

Moderna and Merck shares fell after full results for their personalized melanoma vaccine failed to meet investors’ high expectations. The treatment, intismeran autogene, combines a patient-specific vaccine developed by Moderna with Merck’s immunotherapy Keytruda. In a phase 3 trial, the combination cut the risk of melanoma returning or death by 42% compared with Keytruda alone, and reduced the risk of cancer spreading or death by 38%. After two years, about 82% of patients on the combination were alive without a recurrence, versus 70% on Keytruda alone. Moderna’s shares dropped as much as 25% after partial results leaked, while Merck’s fell about 1%. Analysts called the results clinically meaningful and a strong data set, suggesting the market reaction reflected elevated expectations. Merck CEO Robert Davis said manufacturing can take six weeks, but the company hopes to speed up production and broaden access.