Moderna Inc.’s shares surged by nearly 200% on Wednesday, adding approximately $44 billion to the company’s market valuation, after the biotech firm and Merck & Co. announced that their experimental personalized cancer vaccine met its primary and secondary endpoints in a mid-stage trial.
The trial, which targeted melanoma, evaluated the combination of Moderna’s mRNA-based vaccine with Merck’s Keytruda immunotherapy. The vaccine, designed to train the immune system to recognize and attack cancer cells, was shown to prevent melanoma recurrence and reduce the risk of the cancer spreading elsewhere in the body. Earlier trial data had indicated that the combination therapy reduced the risk of melanoma recurrence or death by 44% compared to Keytruda alone, though the companies have not disclosed the specific efficacy rate or hazard ratios from the latest results.
The vaccine works by using genetic sequencing to identify mutations unique to a patient’s tumor. Algorithms then select up to 34 targets, which are encoded into an mRNA strand to stimulate an immune response. The treatment is administered alongside Keytruda, which is already approved for melanoma and other cancers.
Moderna’s Chief Executive Stéphane Bancel stated that the vaccine would cost less than existing CAR-T therapies, which can exceed $500,000 per patient, though no specific pricing for the vaccine has been provided. The company also noted that the vaccine is being tested in additional cancer types, including lung, kidney, and pancreatic cancers.
The partnership between Moderna and Merck dates back to 2016, when Merck committed $200 million to research the combination. In 2022, the companies formalized a joint development agreement to co-develop the treatment and share profits. Detailed trial results are expected to be presented at a medical conference later this year, with potential U.S. approval targeted for 2027.
Moderna’s stock had previously fallen more than 90% from its pandemic-era peak and was among the most heavily shorted companies in the S&P 500 earlier in 2026. The company’s sales also declined by nearly two-thirds in 2023, underscoring the challenges it faced transitioning from its COVID-19 vaccine dominance to a broader biotech pipeline.
