Recent positive Phase 3 data from Merck and Moderna's joint personalized mRNA cancer vaccine have lifted Moderna shares sharply, yet reinforced the existing collaboration model without signaling a full merger. Merck has pursued smaller, targeted acquisitions such as Terns Pharmaceuticals for roughly $6.8 billion to bolster its post-Keytruda pipeline toward a $70 billion sales goal, consistent with its stated preference for deals under $15 billion. No regulatory filings, earnings disclosures, or corporate communications indicate an imminent combination, supporting the market-implied 72.5% probability against a 2026 announcement. Key catalysts ahead include further vaccine trial readouts and potential partnership expansions, though these appear more likely to sustain the current alliance than trigger acquisition talks.