Moderna and Merck succeed with cancer vaccine. Which of these two stocks offers more potential?
Moderna $MRNA closed on August 19, 2026 at $174.38, up 176.97% from the previous day. It was the largest single-day move in the stock's history and the company's market value jumped from about $25 billion to $69 billion in one session. Merck $MRK added about 12.6% the same day, reaching new all-time highs.
Key points
Same drug, two different bets. Moderna and Merck split the profits from intismeran exactly in half. But one of them collects from each treated patient a second time, and that second payment doesn't appear in the contract at all.
The market didn't buy melanoma. According to JPMorgan, the bank had already priced the success in the study into its model long before the results came out, and its confirmation should have moved the value only slightly. Yet the stock shot up 177%.
Analysts raised price targets by hundreds of percent. Still, even after the most extensive revision in the stock's history, the consensus didn't reach where the price already is. The dispersion of estimates among banks is extraordinary.
Merck will start to see Keytruda erode before biosimilars arrive. The company itself states in its annual report the date from which U.S. sales will decline, and it's a year earlier than usually written. The defense is a single change in the form of administration.
Moderna already used the August jump. Eight days after the results, it announced a $2 billion convertible bond offering and the stock fell that day. The price jump didn't make its shares cheaper; it made something else cheaper.
The reason was a single press release. In the INTerpath-001 study, an mRNA-based cancer treatment succeeded in a final-stage trial for the first time in history, the same technology made famous by COVID vaccines. It is manufactured separately for each patient based on mutations in their own tumor, tested in people after surgical removal of melanoma, and given in combination with Merck's drug Keytruda. Ten years of research that had mainly brought disappointment turned in one morning into the most watched clinical result of the year.
The costs and potential profits from the new therapy are split exactly in half between Moderna and Merck. But the reaction of their stocks was completely different and the difference isn't a market error. One of the two companies expects a new business from the same drug, the other a defense of its existing one. So the decisive factor isn't how good the news is, but how much of it each of the two stocks already carries in its price.
The market paid tens of billions for a result nobody saw
The announcement contained exactly zero numbers about the size of the clinical benefit. Merck and Moderna said that the combination of intismeran autogene with Keytruda statistically significantly and clinically meaningfully improved recurrence-free survival and distant metastasis-free survival compared to Keytruda alone. The study enrolled 1,137 patients who had already had melanoma surgically removed and who now wait to see if the tumor returns. Two-thirds of them received the new therapy along with Keytruda, while the remaining third received only Keytruda, which is today's standard treatment. But the companies did not disclose the hazard ratio or any other measure of how much better the combination was. Data on overall survival, i.e., whether patients ultimately live longer, are missing because the study is still ongoing and continues to follow patients. Detailed results are set to appear at a medical congress.