Merck & Co. (NYSE: MRK) experienced a significant surge on Wednesday, with shares climbing 13.3% to $153.12, a record high. This dramatic increase followed the announcement of positive Phase 3 trial results for a personalized melanoma vaccine developed in partnership with Moderna (NASDAQ: MRNA). The rally added approximately $44.4 billion to Merck's market capitalization, based on its 2.47 billion outstanding shares, bringing its implied market value to around $378.2 billion.
The pivotal study, which enrolled 1,137 patients with high-risk melanoma post-surgery, evaluated the combination of the vaccine, known as intismeran autogene, with Keytruda. The trial met its primary endpoints, showing significant improvement in delaying disease recurrence and distant metastasis compared to Keytruda alone. No new safety signals were reported, though full data has not yet been disclosed.
Moderna's President, Stephen Hoge, described the results as both "clinically significant" and "statistically significant." The companies are currently in discussions with regulatory authorities, with a potential launch anticipated as early as 2027. Pricing details have not yet been finalized.
Investors' reaction suggests they are pricing in more than just the melanoma opportunity. While Barclays forecasts about $3 billion in annual melanoma sales by 2035, and other estimates place the program's value near $2.5 billion, Wednesday's market cap gain was roughly 18 times that figure. This indicates a broader expectation that the vaccine platform could succeed in other tumor types, potentially extending Keytruda's commercial life and mitigating upcoming patent expirations.
Keytruda remains the cornerstone of Merck's earnings, generating $8.37 billion in Q2 2026 sales, which accounted for 50.4% of the company's $16.61 billion total revenue. The vaccine could enhance this franchise by creating new combination therapies. Merck's full-year 2026 sales guidance stands at $66.3-$67.3 billion.
Wall Street analysts were caught off guard by the rally. The average price target prior to the move was $136.04, which is 11.2% below the intraday price. Even the highest target of $155 leaves only 1.2% upside. This suggests that significant estimate revisions are likely as analysts incorporate the new data.
Moderna's stock also experienced a sharp increase, more than doubling on volume that was about 15 times its 50-day average. The two companies share profits from the collaboration equally, reinforcing the platform narrative that investors are embracing.
However, risks remain. The companies have not yet released hazard ratios, survival data, or detailed safety information. Regulatory scrutiny will focus on the individualized manufacturing process, turnaround times, and consistency. Pricing is also undetermined. A weaker full data presentation could unwind some of Wednesday's premium.
Investors now await the full Phase 3 results and a clearer regulatory timeline. Until then, Merck's new record price reflects a belief that the vaccine can become a significant growth driver beyond melanoma.
