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Moderna Crashed 18% Despite Promising Cancer Vaccine Results—What Went Wrong?

Moderna suffered a nearly 18% stock-market decline on October 22, 2026, after clinical data involving its experimental personalized cancer vaccine, intismeran autogene, circulated ahead of a major oncology conference. The treatment, developed alongside Merck (NYSE:MRK), is being evaluated with Keytruda to prevent melanoma from returning after surgery. The reported Phase 3 results indicated a 42% reduction in the relative risk of cancer recurrence or death, exceeding several Wall Street analysts’ expectations. Yet Moderna shares fell to $202.63, despite having rallied more than 500% earlier in the year. The selloff exposed a disconnect between clinical progress and investor expectations, particularly as the company continues to report substantial operating losses while investing in its oncology pipeline.