Moderna plunges by as much as 26%, setting a record for the biggest single-day drop! Melanoma vaccine data leaked early, results fall short of expectations

Phase III clinical trial data for the personalized melanoma vaccine jointly developed by Moderna and Merck was unexpectedly leaked early, and the results did not meet market expectations, causing a significant drop in Moderna's stock price. This data disclosure incident not only dampened investor sentiment but also challenged the long-standing optimism surrounding mRNA cancer therapies.

On Thursday, Moderna's share price plummeted as much as 26% intraday, marking a record single-day drop, before partially rebounding to close down 17.6%; Merck shares closed down 1.8%. As of Thursday’s close, Moderna’s stock price was still up 655% year-to-date.

Data shows that the vaccine can reduce the risk of cancer recurrence by 42% and lower the risk of distant metastasis (tumor spreading to distant organs) by 38%. These results fell short of some investors’ expectations, as the market had previously been highly optimistic about this therapy.

Reportedly, the above data was originally scheduled for official release this Saturday at the European Society for Medical Oncology (ESMO) Annual Meeting in Madrid. However, the information was leaked early via unverified accounts on social media platform X, triggering panic selling in the market. Merck and Moderna later confirmed they would formally announce the complete Phase III trial results of the study named INTerpath-001.

The data leak originated from several unverified accounts on platform X. One account published a report attributed to Oncology Central detailing the trial results, but the website link provided in the report was inaccessible.

As soon as the news spread, Moderna and Merck shares came under pressure and declined, after which both companies confirmed the authenticity of the data leak.

The official name of the vaccine is intismeran autogene, used in combination with Merck’s blockbuster tumor immunotherapy Keytruda.

The trial involved more than 1,100 patients. All participants were high-risk patients for recurrence after melanoma surgery. The combined therapy group was compared with a control group receiving only Keytruda.

The official Phase III data did not reach the higher benchmarks previously referenced by investors.

An earlier study—covering a different patient population and observation period, thus not directly comparable—showed that the combined therapy could reduce the risk of recurrence or death by 49%, and the risk of distant metastasis or death by 59%.

TD Cowen analyst Tyler Van Buren published a client note even before the leak was officially confirmed, stating that the new data showed the therapy’s effect in preventing distant metastasis was “not remarkable” and lagged behind its performance in reducing recurrence rates. He also said more details were needed for a full assessment of the overall results.

In August this year, Moderna and Merck announced that the personalized vaccine had achieved “significant and clinically meaningful” positive results in reducing the recurrence rate of fatal tumors, marking the first ever successful Phase III trial for an mRNA cancer therapy—a news event that sent Moderna’s stock soaring.

At that time, the two companies did not disclose specific data. Once the actual data was released, the gap between market expectations and reality became the direct trigger for the subsequent stock price drop.

Although short-term data disappointed the market, researchers and the oncology community continue to closely follow the long-term potential of mRNA cancer vaccines.

For decades, progress in cancer vaccine development has been repeatedly frustrated, so the successful completion of this Phase III trial still represents a significant milestone.

Currently, Moderna and Merck are conducting multiple expansion studies on this personalized vaccine platform, including clinical trials for lung cancer, bladder cancer, and other tumor types.

This technology can customize vaccines targeting individual tumor gene characteristics and is seen in the industry as a next-generation cancer therapy with broad application potential.