Merck and Moderna’s established 2016 partnership on the personalized mRNA cancer vaccine intismeran autogene, which delivered statistically significant Phase 3 success in melanoma at an August 2026 interim analysis, underpins the 92.2% market-implied probability against a 2026 merger or acquisition announcement. This collaboration already provides 50/50 profit-sharing economics and shared development costs without requiring full corporate integration, while Merck pursues separate transactions such as its $6.7 billion Terns Pharmaceuticals acquisition and a $2.13 billion licensing deal with SciBrunch. Recent Moderna share gains exceeding 170% reflect strengthened standalone oncology prospects. A transaction remains possible if post-Keytruda patent pressures or manufacturing scale challenges prompt consolidation, though current fundamentals favor continued partnership over M&A.