Moderna Shares Fall 25% Following Cancer Vaccine Data Leak

Shares of Moderna experienced a dramatic decline of up to 25% on Thursday, October 22, following an accidental leak of partial clinical data regarding the Merck and Moderna cancer vaccine on an oncology website prior to its official publication. Despite the unusual nature of this Moderna stock plunge—triggered by findings that actually demonstrated positive results—the stock price eventually closed down $43.18, or 17.57%, at $202.63.

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Moderna Stock Drop Follows Cancer Vaccine Data Leak Despite Positive Results

Ultimately, the downward movement appeared to stem from exceptionally high market expectations crashing into concrete figures. Prior to the leak, shares had nearly quadrupled since August, when both companies initially announced the trial’s success without disclosing the underlying numbers. Although this recent downturn eroded a significant portion of that upward trajectory, Moderna maintained a year-to-date gain of approximately 587% at the time of writing, trading within a 52-week range of $22.28 to $254.48.

What The Merck Moderna Cancer Vaccine Trial Showed

Designated as INTerpath-001, the Phase 3 clinical trial evaluated 1,137 melanoma patients following surgical intervention. The therapeutic vaccine, known as intismeran autogene, sequences the distinct mutations present in an individual’s tumor to direct the immune system specifically toward those targets.

When administered alongside Keytruda, the joint treatment reduced the risk of disease recurrence or death by 42%, and lowered the risk of distant metastasis or death by 38%, relative to Keytruda administered alone. Two years post-treatment, 82.2% of patients receiving the combination therapy remained cancer-free, compared to 70% in the monotherapy control group. Furthermore, the risk reduction benefit increased to 58% following the completion of the six-month vaccine schedule. These robust metrics help explain why the sudden drop took observers by surprise.

Dr. Dean Y. Li, president of Merck Research Laboratories, stated:

“INTerpath-001 is the first Phase 3 study to demonstrate a clinically meaningful improvement in RFS and DMFS over standard-of-care KEYTRUDA in patients with resected melanoma, setting a new benchmark in the adjuvant setting and representing one of the most significant advances in melanoma treatment since the advent of immunotherapy. These results, building on the body of evidence from the Phase 2b study, strengthen our confidence in the curative potential of intismeran autogene when given in combination with KEYTRUDA. Importantly, these data suggest that, by intervening earlier, this approach may offer a tangible opportunity to change the trajectory of a patient’s cancer.”

Why The Moderna Stock Price Fell Anyway

Industry analysts largely attribute the sell-off to market expectations rather than scientific shortcomings. Prior to the disclosure, several Wall Street experts indicated that investors had anticipated a risk reduction threshold of 40% or higher, with many having anchored their hopes on the superior efficacy numbers seen in the earlier Phase 2b study, as noted by RBC Capital Markets. While the 42% outcome cleared that hurdle, it did so by a narrow margin. Consequently, the Moderna stock price declined alongside Merck shares, which fell about 1.8%. Moderna dropped from a previous close of $245.81 to an intraday low of $180.80, with approximately 49.8 million shares traded—more than double the standard volume of 20.2 million.

BMO Capital Markets analyst Evan Seigerman attributed the market reaction to inflated projections rather than diminished efficacy, and UBS analysts similarly characterized the dataset as robust. Conversely, Trung Huynh of RBC maintained a more cautious stance, arguing that melanoma should represent the most favorable environment for this type of vaccine.

What Moderna And Merck Plan From Here

Moderna CEO Stéphane Bancel announced that both organizations are preparing regulatory filings for U.S. approval, with a commercial launch targeted for 2027. The complete trial data is scheduled for an official presentation at the ESMO Congress in Madrid, and both companies are concurrently evaluating the combination therapy across kidney, bladder, and lung cancers. Nevertheless, this long-term outlook provided little immediate relief to the stock price on Thursday.

Stéphane Bancel, Chief Executive Officer of Moderna, shared the following remarks:

“From the beginning, we believed mRNA technology could make it possible to develop cancer treatments uniquely matched to each patient’s tumor. The INTerpath-001 results mark a defining moment for that vision and show what’s possible when we rethink how medicines are made. These results reinforce our conviction that mRNA has the potential to fundamentally change how we treat cancer.”

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At present, the market reaction reflects the lofty benchmarks established by investors rather than any flaw in the therapeutic candidate. Shareholders who purchased near peak levels and navigated the recent downturn will likely focus on upcoming data releases in other oncology indications, as well as Moderna’s scheduled earnings report on November 6, which could introduce further volatility to the stock price.

Frequently Asked Questions

What caused the drop in Moderna’s stock price?

The drop of up to 25% was triggered by a premature data leak of the Merck Moderna cancer vaccine trial on an oncology website, combined with investor expectations that had been set higher than the reported 42% risk reduction.

What were the key results of the INTerpath-001 trial?

The Phase 3 trial showed that pairing the Moderna cancer vaccine (intismeran autogene) with Merck’s Keytruda cut the risk of melanoma recurrence or death by 42% and the risk of distant spread or death by 38% compared to Keytruda alone.

When do Moderna and Merck plan to launch the vaccine?

The companies are preparing to file for U.S. approval and anticipate launching the cancer vaccine in 2027.

Are the companies testing the vaccine on other types of cancer?

Yes, Moderna and Merck are also evaluating the combination therapy in kidney, bladder, and lung cancers.

When will the full trial data be officially presented?

The full data set is scheduled for its formal debut at the ESMO Congress in Madrid.