Merck & Co. stock trades just below record high after cancer vaccine breakthrough

Merck & Co. (US58933Y1055) stock has been changing hands in the high $140s in August 2026, standing only a few dollars below a reported all-time high of $153.53 after strong Phase 3 melanoma cancer vaccine data with a partner sparked a sharp rally and pushed the shares into record territory as of August 20, 2026. The same recent coverage notes that Merck’s shares opened at $152.21 on August 20, 2026, reflecting a 12.6% gain versus a prior reference level and underscoring how the vaccine news has reset expectations for the company’s oncology franchise.

Cancer vaccine data lifts Merck

Recent reports describe how a personalized mRNA cancer vaccine for melanoma, used together with Merck’s immunotherapy drug Keytruda, achieved its primary endpoint in a large Phase 3 trial, contributing to a broad move higher in both the vaccine partner and Merck on August 20, 2026. One overview notes that this data helped drive Merck’s stock up 12.6% to an opening price of $152.21 during that session, with intraday trading taking the stock to a new all-time high of $153.53 before it settled lower by the close on the New York Stock Exchange. Additional market commentary points out that as of August 21, 2026, Merck’s shares were quoted around $149.25 to $149.36 in US trading, just below a 52-week high of $153.50, indicating that investors have continued to price in a stronger growth outlook following the melanoma vaccine success.

Internationally, related coverage highlights that Merck’s stock has been supported across venues, with compiled quotes showing the company’s shares near $149 in the US market while European listings changed hands in a range of EUR 128.40 to EUR 131.60 on August 21, 2026. Another market snapshot emphasizes that the stock’s recent move has pushed it to the top of its 52-week range, with one report citing a high of $153.68 on August 21, 2026, which is described as the highest level of the past 52 weeks and signals how the cancer vaccine data has propelled the shares into uncharted territory for this cycle.

Valuation, targets and comparison

Alongside the rally, valuation discussions have intensified, with one analysis framework putting Merck’s so-called fair value measure at $119.88 while indicating that the stock was trading at $152.55, a premium of 27.3% over that intrinsic value estimate, as of late August 2026. A separate recent overview cites a 12-month average price target of $150.20 for Merck stock as of August 20, 2026, compared with a spot price of around $150.39 at that time, implying a modest downside of 0.73% relative to the average target even after the rally. This contrast between the stock’s record high of $153.53 and the consensus target in the mid-$150 range illustrates how quickly expectations for the melanoma vaccine and broader oncology pipeline have been repriced in the wake of the Phase 3 data.

Another piece of market commentary notes that as of August 20, 2026, Merck’s stock closed at $148.99 on the New York Stock Exchange, with a small post-market move to $149.00 by 7:59 p.m. ET, compared with the earlier intraday high above $150, highlighting intraday volatility around the news. The same overview underscores that the 12.6% gain into the $152.21 opening level on August 20, 2026, marked Merck’s strongest single-day advance in many years and pushed the stock’s year-to-date performance into a gain of more than 40% on some European platforms, outpacing a sector performance in the low 20 percent range over the same period.

Keytruda and oncology franchise

For investors, the core of the story remains Merck’s immuno-oncology flagship Keytruda, which already generates significant revenue and has a broad clinical program across multiple tumor types. The new melanoma vaccine data, in which the mRNA-based personalized vaccine was administered alongside Keytruda, reinforces the idea that Merck can extend Keytruda’s lifecycle and defend its position in melanoma as patent expiries approach by pairing it with next-generation immunotherapy combinations. Recent commentary notes that the melanoma trial success has revived broader interest in cancer vaccines and is viewed as a key milestone for leveraging mRNA technology beyond infectious disease vaccines in oncology.

The same discussions suggest that Merck’s medium-term growth profile could be supported not only by incremental indications for Keytruda but also by new oncology assets that benefit from the company’s experience with immunotherapy combinations. As investors reassess Merck’s pipeline, the magnitude of the August 20, 2026 reaction suggests that the market is attributing a meaningful probability of future revenue streams from the melanoma vaccine partnership, with the intraday move to the $153.53 all-time high serving as a visible signal of that optimism.

Product spotlight: Keytruda in melanoma

Merck’s immunotherapy drug Keytruda, used in combination with the personalized melanoma vaccine in the successful Phase 3 trial, is already approved for multiple cancers, including certain types of melanoma, and has become one of the world’s best-selling oncology medicines. In the context of the new trial, Keytruda served as the immunotherapy backbone, with the mRNA vaccine designed to train the patient’s immune system to target tumor-specific mutations, a concept that builds on earlier success in adjuvant melanoma treatment. The latest Phase 3 data now suggests that adding the vaccine to Keytruda can reduce the risk of cancer returning in high-risk melanoma patients compared with Keytruda alone, strengthening the case for combined immunotherapy and vaccine strategies in this setting.

Merck & Co. stock level

According to recent trading summaries, Merck & Co. stock closed at $148.99 on the New York Stock Exchange on August 20, 2026, with a brief post-market quote of $149.00 at 7:59 p.m. ET, and subsequent intraday references on August 21, 2026 pointing to levels around $149.25 to $149.36 as the stock hovered just below a stated 52-week and all-time high in the mid-$150 range.

Fact box

Company: Merck & Co., Inc.
ISIN: US58933Y1055
Ticker: MRK
Exchange: New York Stock Exchange
Price (as of August 20, 2026, 7:59 p.m. ET): $149.00 USD
Sector / Industry: Pharmaceuticals / Biotechnology
Index membership: S&P 500