Moderna’s dramatic ascent this year has been fueled by optimism that its personalized cancer vaccine could reshape oncology and redefine the company beyond its pandemic-era success. That promise may soon become a reality.
A treatment combining Moderna’s intismeran autogene vaccine and Merck’s blockbuster immunotherapy drug Keytruda is more effective than Keytruda alone in preventing the recurrence of skin cancer, the companies said Wednesday.
A trial of 1,100 patients found that the combination helped people stay cancer-free longer than standard treatment after having their melanoma surgically removed. The results marked the first Phase 3 trial success for a cancer vaccine, meaning Moderna and Merck can now ask regulators to approve the treatment for marketing.
Moderna shares surged 177% on Wednesday, marking their largest daily percentage increase on record and eclipsing gains from premarket trading, when shares rose as high as 112%.
Merck, meanwhile, advanced nearly 13% to clinch a record closing high and its largest same-day percentage increase since March 2009, according to Dow Jones Market Data.
Fellow vaccine makers also got a boost, as Novavax and U.S.-listed shares of BioNTech rose 11% and 22%, respectively.
The magnitude of the move is easy to understand for Moderna, given its struggle to shake its reputation as a Covid-and-flu company. The biotech shot to prominence at the height of the pandemic, when it delivered the second Covid vaccine approved by U.S. regulators.
That product, Spikevax, remains a cornerstone of Moderna’s portfolio, even as revenue dwindles. Moderna’s flu portfolio also remains a major contributor to its top line. However, investors are holding out for a true breakthrough: a high-impact product that can lift the stock back toward its 2021 highs.
Consequently, attention has turned to Moderna’s intismeran autogene. Shares rose steeply in June when Moderna and Merck jointly reported positive five year follow-up data in a Phase 2 trial. Cancer recurrence or death was halved among patients who had received the vaccine-Keytruda combination.
Heading into Wednesday’s session, Moderna stock had risen nearly 114% in 2026, far outpacing the broader market as well as the biotech sector. The iShares Biotechnology exchange-traded fund, which tracks the industry’s largest players, has gained 21% this year.
Much of Moderna’s momentum has hinged on expectations for the customized cancer vaccine, and investors are treating the latest data as proof the narrative is turning. Wednesday’s stock surge could be just the start.
Crucially, the late-stage trial success offers validation of Moderna’s patented mRNA platform, offering a major win at a time when the technology faces scrutiny from regulators including Health and Human Services Secretary Robert F. Kennedy Jr.
Kennedy announced the cancellation of contracts worth around $500 million in August 2025, citing false claims that the vaccines led to “new mutations.” He has previously asserted that mRNA technology poses more risks than benefits.
Moderna, separately, encountered regulatory friction around mFlusiva, its recently cleared flu vaccine for adults aged 50 and above. The approval resolved months of tense exchanges stemming from the Food and Drug Administration’s refusal to accept the application for review in February.
While intismeran autogene has yet to enter formal regulatory review, the latest data are a promising sign Moderna’s mRNA technology can be applied to other diseases. Past trials have shown the Keytruda combination has a manageable safety profile and is generally well-tolerated.
Jefferies analyst Andrew Tsai views the trial outcome as proof of Moderna’s mRNA platform, which he expects to raise Wall Street expectations for the company’s entire oncology pipeline and various other solid tumor trials.
The trial achieved statistical significance for both its primary endpoint of recurrence-free survival and secondary endpoint of distant metastasis-free survival, Tsai noted. Respectively, these measure how long patients remain cancer-free after tumor removal and how long before the cancer spreads to distant organs.
Looking ahead, Tsai anticipates Moderna could be marketing over seven products across respiratory, oncology, and rare diseases by 2027, which would “help reduce annual cash burn and ensure 2028 cash breakeven.” Intismeran represents yet another potential growth driver.
The vaccine’s success is also important for Merck as it works to blunt future revenue loss. Keytruda, the world’s best-selling drug as recently as last year, has come into focus ahead of its looming 2028 patent cliff. At that point, key protections will expire and a flood of copycat products will enter the market.
Drawing on its success in oncology, Merck has partnered with other drugmakers including China’s Sichuan Kelun-Biotech Biopharmaceutical, to develop several preclinical candidates.
In May, Kelun-Biotech reported positive results in a late-stage trial evaluating one of those candidates, sacituzumab tirumotecan, in combination with Keytruda. The joint treatment improved progression-free survival in patients with advanced non-small cell lung cancer versus Keytruda alone.
The latest data from Merck and Moderna carry broader significance, as they address a critical unmet need for patients. For decades, researchers have struggled to develop vaccines that help the immune system fight cancer, with limited success.
For Moderna, intismeran represents a move past respiratory vaccines into uncharted territory: a shift into next-generation, personalized treatments, and a bold strategic leap into oncology following over a decade of research. Besides melanoma, Moderna is also testing the vaccine against cancers of the lung, bladder, kidney, stomach and pancreas.
Unlike other treatments, intismeran is designed for early-stage intervention. As scientists at Merck and Moderna recently told Barron’s, administering intismeran as a postsurgical adjuvant hits the cancer when the immune system is best equipped to fight it.
Approval of Intismeran would introduce an unprecedented, ultra-personalized “market-of-one” therapy. Using Moderna’s messenger-RNA technology, the companies individualize the vaccine to flag dozens of mutations that are unique to each patient’s tumor. That customization makes the product quite different from the off-the-shelf drugs and vaccines previously sold by the companies.
While similar treatments have cost millions per dose, Moderna has automated the manufacturing process, leading analysts to believe it can scale up to serve billions of dollars worth of annual sales.
The Phase 3 findings are encouraging, but Wall Street has several unresolved questions. While the results were statistically significant, the drugmakers failed to disclose measures like confidence intervals and hazard ratios, which could help determine the true magnitude of the clinical benefit.
Citi analyst Geoff Meacham also raises the question of whether the vaccine’s efficacy translates across tumor types.
More detailed data are expected at an international medical meeting. While details remain scarce for now, Barclays analyst Eliana Merle suspects the trial was designed with a very high standard for success, which bodes well for the vaccine’s success across other indications.
Merle assigns a 60% probability of success to intismeran’s path through late-stage trials, regulatory approval, and commercialization. If successful, she projects peak annual sales of $3 billion by 2035.
“Success in melanoma would help validate other indications and, we think, drive credit to larger market sizes,” Merle wrote.
Moderna and Merck plan to present their findings to federal health authorities to get approval to market the combination therapy. For a company eager to prove it is much more than a pandemic success story, this novel treatment might be the ultimate proof of concept.