Merck and Moderna cancer vaccine data leak shows modest benefit, shares slide

A data leak ahead of the European Society of Medical Oncology meeting revealed early results for the personalized cancer vaccine intismeran autogene combined with Merck's Keytruda. The information appeared online briefly before being removed, prompting immediate market reaction.

The leaked figures indicated a recurrence‑free survival hazard ratio of 0.58, translating to a 42% reduction in the risk of recurrence or death. Additionally, 82.2% of patients receiving the combination were reported alive after two years, compared with roughly 70% in historical controls.

Analysts had hoped for a stronger signal, particularly a hazard ratio below 0.60, to suggest broader efficacy beyond melanoma. The modest improvement fell short of elevated expectations, leading to a drop in Merck and Moderna shares and a cautious outlook from investors.