Moderna Shares Plunge 20% After Premature Leak of Skin Cancer Vaccine Data

Moderna shares plummeted over 20% on Wall Street, reaching a sharp intraday drop of nearly 25%, following a premature leak of Phase 3 clinical trial data for its personalized cancer vaccine. Partner company Merck experienced a milder decline of about 3%.

The turmoil was triggered by the early publication of trial data on the medical website Oncology Central, which was removed shortly afterward. The complete results were officially scheduled to be unveiled during the weekend at the European Society for Medical Oncology (ESMO) congress in Madrid, but the leak provided investors with a premature glimpse at efficacy data.

Clinical Results vs. Expectations

According to the leaked report, the combination of Moderna and Merck's experimental vaccine with the immunotherapy drug Keytruda reduced the risk of melanoma recurrence or death by 42% compared to Keytruda alone. Furthermore, the data showed that after two years, 82.2% of patients receiving the combination therapy remained alive and cancer-free, compared to 70% for those treated with Keytruda alone.

"The leaked data sparked aggressive selling despite positive clinical outcomes, as Wall Street immediately compared the results to Phase 2 data which had shown a 49% risk reduction."

Financial Impact and Outlook

For Moderna, battling a collapse in revenues from the COVID-19 era and a Q2 net loss of $782 million against just $145 million in revenue, this vaccine is a critical growth engine. Analysts at Barclays estimate the melanoma treatment could generate $3 billion by 2035 and serve as a foundation for other cancer therapies.

Investors are now holding their breath for the official presentation of the full data in Madrid, which will determine whether the current drop was an overreaction or a signal that the path to regulatory approval in 2027 will be fraught with hurdles.