Moderna shares drop sharply after reported premature release of cancer vaccine trial data

Moderna’s stock plunged on Thursday after a market report said early results from closely tracked cancer vaccine clinical trials appeared to have been released ahead of schedule, triggering a fast selloff. Moderna shares fell more than 25% in the session, according to the report.

The selloff extended beyond Moderna. Merck shares were also reported to have declined, falling over 3% on the same day, in a move that suggested investors were reacting broadly to the implications of the contested timing around clinical data disclosures.

The episode centered on experimental cancer vaccine programs. In the report, the pricing shock was linked to what was described as an “apparent” data leak or early posting of trial information that the market had been expecting through formal communications.

Because the reporting described the release as apparent rather than confirmed through an official filing or press release in the account provided, it left open key questions about what exact documents were posted, who posted them, and whether the information was complete, preliminary, or subject to later amendment.

For Moderna, the market reaction underscores how tightly investors watch the cadence and content of clinical trial updates, especially in oncology, where efficacy and safety indicates can swing expectations for future development costs, regulatory timing, and potential partnership value.

Merck’s concurrent move also highlights the sector sensitivity of oncology vaccine and immunotherapy programs. Even when the underlying assets differ, investors often reprice a broader set of expectations for pipeline performance when headline trial information hits the tape.

As of the information available from the market report, Moderna did not publicly clarify in the account provided whether it had identified the source of the early posting, corrected any errors, or how the company planned to address the timing around the data release.