Moderna Stock Drops 25% on Cancer Vaccine Report Nobody Has Confirmed

Moderna shares fell more than 25% after what appears to be an early release of cancer vaccine data. Merck shares dropped more than 3% on the same news, according to Investing.com, which reported the move on October 22, 2026.

The product at the center of the sell-off is intismeran autogene. You may also see it called mRNA-4157 or V940. It is a personalized cancer vaccine built on messenger RNA, a type of genetic instruction. Moderna and Merck are developing it together, and it is being tested alongside Merck's cancer drug Keytruda (pembrolizumab).

The most recent formal update came on August 19, 2026. Moderna and Merck announced that a large late-stage trial, called INTerpath-001, had met its goals for melanoma. Those goals were recurrence-free survival, meaning how long patients go without the cancer returning, and distant metastasis-free survival, meaning how long they go without it spreading to other parts of the body. The announcement came in a joint statement from Moderna. Reuters reported that the results came from an interim analysis, which is a look at the data before the trial is finished.

Moderna shares rose as much as 160% during that trading day, and Merck shares jumped 12%. The next day, Fierce Biotech reported that Moderna had closed up 177%.

The August result was the latest step in a long process. Moderna and Merck reported Phase 2b results from the KEYNOTE-94 study in December 2022, when the combination met its main goal. In December 2023, the companies started the bigger Phase 3 trial, INTerpath-001, which asks whether the vaccine plus Keytruda works better than Keytruda alone. In January 2026, Merck reported five-year data showing sustained improvement in recurrence-free survival. Earlier five-year data from a mid-stage trial, presented in June, showed the vaccine cut the risk of cancer returning by half, per Reuters.

The program is wide as well as long. Merck describes INTerpath as nine Phase 2 and Phase 3 trials covering several tumor types and stages of disease. Keytruda is used against 20 kinds of cancerous tumors and 45 types and stages of cancer, according to Reuters. So a melanoma result sits inside a much larger picture.

In my view, that breadth is part of why the August moves were so big. The October move is a different kind of event.

A scheduled announcement comes with a defined set of data and a company statement. The October report, as far as the coverage shows, came with neither. Investors had to weigh two things at once: what the material says, and how much to trust information the company has not formally presented. A 25% one-day drop in Moderna suggests the market took that doubt seriously, even before anyone knows what an official update would show. Merck's smaller fall points the same way, though the two moves can't be compared directly, because the companies' stakes in the program differ.

For someone following the stock, the sensible reading is narrow. The August result rested on an interim look at the data. Neither that fact nor the October report tells you what the next formal results will show, or when they will arrive. In my view, a stock this sensitive to one clinical program is going to swing hard on news like this. It is a bit like a pass-or-fail exam: the outcome can change the price sharply in either direction, and the price is simply reflecting that.