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Why Moderna Stock Plunged After Its Melanoma Vaccine Results Leaked
Moderna fell as much as 26% intraday on Oct. 22, 2026, then closed down 17.57%, even though intismeran plus Keytruda reduced recurrence or death risk by 42% in Phase 3.
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Key takeaways
- Moderna fell as much as 26% intraday on Oct. 22, 2026, then closed down 17.57%, even though intismeran plus Keytruda reduced recurrence or death risk by 42% in Phase 3.
- The trial also improved two year recurrence free survival to 82.2%, versus 70% with Keytruda alone; the results do not establish longer overall survival.
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openai.comCreate a landscape editorial hero image for this Studio Global article: How did the leaked Phase 3 results for Moderna and Merck’s personalized melanoma vaccine intismeran plus Keytruda trigger Moderna’s record i. Article summary: The leak triggered a sharp reassessment of Moderna’s already-rallied stock, rather than revealing a failed trial: intismeran plus Keytruda significantly improved recurrence-free survival, but the reported 42% risk reduct. Topic tags: general, general web, news, user generated. Style: premium digital editorial illustration, source-backed research mood, clean composition, high detail, modern web publication hero. Use reference image context only for broad subject, composition, and topical grounding; do not copy the exact image. Avoid: logos, brand marks, copyrighted characters, real person likenesses, fake screenshots, UI text, readable text, watermarks, charts w
Moderna’s October 22, 2026, plunge was a sharp investor reaction to leaked Phase 3 results—not evidence that the melanoma vaccine trial had failed. Intismeran plus Keytruda met key trial endpoints, but investors weighed the 42% reduction in recurrence-or-death risk against a 49% reduction reported in an earlier, smaller study and Moderna’s enormous run-up that year. 10
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Moderna’s intraday plunge and closing loss
Moderna shares fell as much as 26% during the session, a decline described in coverage as the largest intraday drop in the company’s history. The stock later recovered part of its loss, closing at $202.63, down $43.18, or 17.57%. 10
The market-value figures also reflect different points in the session: Reuters reporting put the loss at about $24 billion during the selloff, while more than $17 billion had been erased by the close. The same report noted the stock had risen more than 500% that year. 10
The selloff continued into Friday, October 23, according to reports that Moderna shares extended their decline. The available reporting does not establish a Friday rebound or a reliable final share-price figure, so the clearest documented partial recovery is the one before Thursday’s close.
How the leak changed the news cycle
Results appeared on the cancer-news website Oncology Central at about 12:30 p.m. Eastern, ahead of the planned ESMO Congress presentation in Madrid. The report was taken down shortly afterward. 5
After the early disclosure, Moderna and Merck released detailed results on Thursday rather than waiting for the scheduled conference presentation. The full INTerpath-001 findings were presented at ESMO on October 24. 13
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What the Phase 3 trial found
INTerpath-001 studied intismeran autogene, an investigational individualized mRNA-based therapy, with Keytruda in patients with completely resected stage IIB–IV melanoma. The trial enrolled 1,137 patients. 18
At a median follow-up of 24.6 months, the combination reduced the relative risk of recurrence or death by 42% compared with Keytruda alone (hazard ratio 0.58). It also reduced the risk of distant metastasis or death by 38% (hazard ratio 0.62). 18
Two-year recurrence-free survival was 82.2% with intismeran plus Keytruda and 70% with Keytruda alone—an absolute difference of 12.2 percentage points. Those rates describe the share of patients who remained recurrence-free; they are not the same measure as the 42% relative risk reduction. 17
These findings are encouraging, but recurrence-free survival is not proof of longer overall survival. The supplied trial reports do not establish that the treatment improves overall survival, so that remains an important unanswered question. 18
Why investors sold despite positive results
Analysts described the decline as a “sell-the-news” reaction after a months-long rally that had lifted Moderna more than 500% that year. A large prior gain can leave a stock especially exposed when new results fail to exceed investor expectations, even when the trial meets its endpoints. 12
The Phase 3 result also drew comparisons with the 49% risk reduction reported in a smaller Phase 2 study. That difference helps explain why the headline number disappointed some investors, but the figures alone do not show that the treatment’s effect weakened: the studies were not the same trial, and a direct comparison needs to account for differences in study design and participants. 2
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The melanoma findings do not establish that intismeran will work in other types of cancer. Broader effectiveness, longer-term outcomes and which patients benefit most remain open questions; the results reported here answer only what was tested in this melanoma trial. 18
What the results mean—and what they don’t
The clinical significance is that adding an individualized mRNA therapy to Keytruda improved recurrence-related outcomes after surgery in this Phase 3 melanoma trial. The data offer evidence of benefit in the studied setting, but they do not by themselves establish longer survival or a new standard of care. 18
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The October 24 ESMO presentation allowed the full findings to be discussed beyond the premature online report. Any move from trial results to routine treatment would still depend on the evidence, regulatory decisions and the patient population ultimately considered appropriate; the sources available here do not establish a regulatory approval. 18
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What is the short answer to "Why Moderna Stock Plunged After Its Melanoma Vaccine Results Leaked"?
Moderna fell as much as 26% intraday on Oct. 22, 2026, then closed down 17.57%, even though intismeran plus Keytruda reduced recurrence or death risk by 42% in Phase 3.
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Moderna fell as much as 26% intraday on Oct. 22, 2026, then closed down 17.57%, even though intismeran plus Keytruda reduced recurrence or death risk by 42% in Phase 3. The trial also improved two year recurrence free survival to 82.2%, versus 70% with Keytruda alone; the results do not establish longer overall survival.