Moderna shares closed at $202.63 on Wednesday, a decline of 17.57%, following reports of a partial data leak regarding its personalized melanoma vaccine. The stock was briefly halted during the day as the news spread.
The leaked data reportedly indicated that Moderna's intismeran autogene, when used with Merck's immunotherapy drug Keytruda, reduced the risk of recurrence or death in certain melanoma patients by 42% compared with Keytruda alone. This statistic was lower than the 49% decline shown in previous Phase II results. Full Phase III results were not scheduled for detailed release until Saturday.
Broader markets also declined, with the S&P 500 falling 1.22% to 7,663 and the Nasdaq Composite losing 2.60% to close at 26,009. In the biotechnology sector, Novavax shares dropped 9.26% to $9.99, while BioNTech fell 1.77% to close at $89.67.
Despite the sharp drop on Wednesday, Moderna stock has risen more than sixfold in 2026. The company, which went public in 2018, has grown 989% since its initial public offering. Investors are now waiting for the full Phase 3 presentation and data from the European Society for Medical Oncology conference scheduled for October 24.