Merck Shares Jump 12.6% on Melanoma Vaccine Trial Results
Merck & Co. (MRK) closed at $152.20 on Wednesday, August 19, 2026, up 12.60% (+$17.03) after the company and partner Moderna (MRNA) announced positive late-stage trial results for their personalized cancer vaccine. The stock touched an intraday high of $153.50, a new 52-week high, before settling slightly lower. After-hours trading saw the stock add another $0.80 to $153.00.
The rally was driven by data from a Phase 3 trial evaluating mRNA-4157 (V940) in combination with Merck’s Keytruda for the adjuvant treatment of high-risk melanoma. The companies reported that the combination significantly improved distant metastasis-free survival compared to Keytruda alone. The news sent Moderna shares soaring 176.97% during the session, according to CNBC, which first reported the results about 11 hours before the market close.
Why This Trial Result Matters Beyond Melanoma
This is not just another oncology win. The trial is one of the first late-stage validations of a personalized mRNA cancer vaccine—a platform that could be applied across multiple tumor types. Merck’s decision to partner with Moderna, rather than develop its own mRNA technology, signals a strategic bet on external innovation. The positive readout strengthens that bet and could unlock a new revenue stream for both companies.
Merck’s market capitalization now stands at $375.50 billion, reflecting the market’s reassessment of its growth outlook. The company’s P/E ratio of 121.56 is elevated, but that is partly due to a one-time gain or accounting adjustment; the forward earnings picture will be clearer when the company reports full quarterly results. Merck’s quarterly dividend of $0.85 per share (yield 2.23%) remains intact, but investors are clearly paying more for growth than income right now.
Stock Performance: A 52-Week High and a Bullish Setup
Wednesday’s move pushed Merck to a 52-week high of $153.50, a level that could attract technical buyers. The stock had traded as low as $77.58 over the past year, meaning it has more than doubled from its bottom. The opening price was $146.94, and the daily low was $144.90, indicating strong buying pressure throughout the session.
For context, Merck’s pharma peers have seen mixed performance. Johnson & Johnson (JNJ) traded at $273.41, up 0.85%, while Pfizer (PFE) rose 3.60% to $28.24. AbbVie (ABBV) gained 2.72% to $265.97. Merck’s outperformance highlights how a single catalyst can re-rate a large-cap stock.
Quarterly Financials Show Revenue Growth, Earnings Beat
Merck reported second-quarter 2026 revenue of $16.61 billion, up 5.07% year-over-year. The company also beat earnings expectations in Q3 2025, with a +9.85% EPS surprise and a +1.76% revenue surprise. That track record of execution, combined with the vaccine catalyst, gives analysts reason to raise price targets.
However, the vaccine is not yet approved. Regulatory filings and eventual commercial launch are still years away. The financial impact will depend on pricing, reimbursement, and manufacturing scale. Moderna’s manufacturing expertise will be crucial, as personalized vaccines require rapid turnaround from biopsy to treatment.
What to Watch: Regulatory Filings and Keytruda Patent Cliff
The next major catalyst for Merck will be the presentation of full trial data at an upcoming medical conference, likely within months. Investors should also watch for the company to file for FDA approval, which could happen in 2027. A key number to monitor is the hazard ratio for distant metastasis-free survival—if it shows a meaningful improvement, the case for approval strengthens.
Beyond the vaccine, Merck faces a looming patent cliff for Keytruda in the late 2020s. The success of this vaccine could partially offset that revenue loss. Watch for any announcements about expansion into other cancer types, as that would broaden the opportunity. The next quarterly earnings call, expected in late October 2026, will provide updated guidance and possibly more details on the vaccine’s commercial roadmap.
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