Moderna Stock Plummets 22% After Cancer-Vaccine Data Leak -- Barrons.com

By Mackenzie Tatananni

Moderna stock cratered on Thursday following a data leak for the cancer vaccine candidate the drugmaker is co-developing with Merck.

The data, which was set to be presented at the annual meeting of the European Society for Medical Oncology over the weekend, was reported by the oncology news website Oncology Central. While the article was pulled, the information quickly circulated on social media, followed by a steep drop in the stock price.

The European Society for Medical Oncology confirmed the leak in a statement, saying the embargo on the study abstract "has been breached," and lifted the embargo on the full dataset Thursday afternoon.

Moderna shares sank 22% to $192.70 on Thursday, heading toward their largest single-day percentage decline on record, according to Dow Jones Market Data. Trading was briefly paused due to volatility. Merck shares, meanwhile, ticked down 0.6%.

Attention centered on the hazard ratio for recurrence-free survival -- the timeframe from assignment to a treatment group until the disease returns or a patient dies from any cause -- which was reported at 0.58.

That figure reflects a 42% reduction in the risk of recurrence or death when adding the candidate vaccine, intismeran autogene, to Merck's blockbuster immunotherapy, Keytruda, compared to Keytruda alone in high-risk melanoma patients.

A hazard ratio of 1.0 would suggest there was no difference between the two groups, while a ratio below 1.0 indicates that patients given the combined treatment faced a lower risk of cancer recurrence or death, suggesting a protective benefit.

Heading into the European Society for Medical Oncology meeting, the most recent hazard ratio for recurrence-free survival from the earlier Phase 2b trial was 0.51 after roughly five years. Moderna stock previously surged following a partial Phase 3 readout in August, though full, detailed data was set to be presented at the conference.

Despite Thursday's stock decline, the reported hazard ratio was better than what several analysts had anticipated.

UBS analyst Michael Yee had previously posited that Moderna stock could rally between 10% and 20% on a hazard ratio of 0.65 for recurrence-free survival, translating to a roughly 35% reduction in the risk of melanoma recurrence or death.

Other market analysts shared similar expectations. William Blair analyst Matt Phipps indicated that a ratio of 0.70 or lower would be well received, while Leerink Partners analyst Daina Graybosch targeted a number under 0.60, describing it as a potentially transformative outcome.

William Blair analyst Myles Minter offered an explanation. "There appears to be a sell-the-news reaction playing out here," Minter wrote, noting that shares remain up over 500% this year even when factoring in the downward move on Thursday.

Ultimately, while it may be "great data," Minter expects investors to continue debating "the fundamental valuation here of what intismeran could be across tumor types." Researchers are currently evaluating the treatment across nine trials in various solid tumors.

There's also the possibility that the underlying numbers were more nuanced. Beyond recurrence-free survival, the combination lowered the risk of cancer spreading to distant organs or tissues by 38%. While encouraging, TD Cowen analyst Tyler Van Buren pointed out that the figure fell short of Wall Street's lofty expectations.

Write to Mackenzie Tatananni at mackenzie.tatananni@barrons.com

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October 22, 2026 15:39 ET (19:39 GMT)