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Moderna shares continued to slide on Friday (October 23, 2026), after dropping nearly 18% in the previous session, despite positive late-stage results for its personalized melanoma vaccine developed with Merck. Investors appeared disappointed that the findings did not fully match the high expectations built around the experimental cancer treatment.
The vaccine, intismeran autogene, is being developed alongside Merck’s Keytruda immunotherapy. The companies released detailed Phase 3 trial results on Thursday after the study's information appeared online ahead of its scheduled presentation. The data showed meaningful benefits for patients, but the market reaction remained negative.
The Phase 3 trial involved more than 1,100 patients with high-risk melanoma. The results showed that Moderna’s vaccine combined with Keytruda reduced the risk of cancer recurrence or death by 42% compared with Keytruda alone.
The treatment also reduced the risk of distant cancer spread or death by 38%. After two years, 82.2% of patients who received the combination remained cancer-free, compared with 70% of those treated with Keytruda alone.
The findings mark an important step forward for personalized cancer treatment. The vaccine targets mutations specific to an individual patient’s tumor, helping the immune system recognize and attack cancer cells.
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The market reaction reflects expectations that had risen sharply after Moderna announced encouraging interim results in August. Those findings sent the company’s shares soaring, but investors had been waiting for detailed data to assess the treatment’s potential.
Analysts said the latest results were encouraging but did not provide enough evidence to support some of the market’s more ambitious expectations, particularly about the vaccine’s potential across other cancer types.
Moderna shares had climbed substantially in the months leading up to the data release. The latest sell-off suggests some investors took profits once the results became public, a pattern often described as a “sell-the-news” reaction.
Merck, which is developing the treatment with Moderna, also saw its shares decline following the results, although its losses were more limited. The company’s broader pharmaceutical business provides a different revenue base from Moderna’s, which remains heavily focused on rebuilding growth beyond its COVID-19 vaccine business.
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Moderna and Merck are preparing to seek US regulatory approval, with a potential launch targeted for 2027. The companies are also studying the approach in other cancers, although its effectiveness beyond melanoma remains uncertain. For investors, the next key questions are whether regulators approve the treatment and whether it can become a commercially successful product.
