Melanoma mRNA Vaccine Data Allegedly Leaked, Moderna Plunges Over 25% in Single Day
nashnova research
Moderna plunged over 25% — its largest single-day drop ever — after clinical data for its melanoma mRNA vaccine apparently leaked early; the market is repricing expectations that had run ahead of the numbers.
What happened?
On Thursday, oncology website OncologyCentral appeared to publish partial study results early. Screenshots spread rapidly on X.
The data was scheduled for formal release on Saturday at the European Society for Medical Oncology (ESMO) annual meeting in Madrid.
Moderna shares fell over 25% on the day, a record single-session decline. Merck also dropped.
What did the leaked data show?
Per Bloomberg, the vaccine — intismeran autogene — combined with Merck's blockbuster drug Keytruda reduced the risk of melanoma recurrence or death by 42%.
An earlier study on a different patient group over a different observation period had shown a 49% reduction in recurrence or death and a 59% reduction in distant metastasis or death.
This means → the new figure is lower, but the two studies used different patient populations and timeframes and cannot be directly compared.
Why did the market react so sharply?
In August, Moderna and Merck announced the vaccine had achieved "significant and clinically meaningful" positive results — but disclosed no specific numbers. The stock rallied.
In plain terms = August gave the market a conclusion with no data. Investors filled in their own optimistic assumptions; the actual numbers fell short of that mental picture.
This reflects a recurring pattern: when a company releases qualitative claims but withholds quantitative data, the expectation gap gets priced in all at once when numbers finally surface.
Is there even disagreement on the decline itself?
As of the report, Moderna was down roughly 25%.
For Merck, Bloomberg reported a 3.9% drop while the Wall Street Journal put it at 1.5% — a notable discrepancy between the two outlets.
Moderna, Merck, ESMO, and OncologyCentral all declined or did not respond to requests for comment.
What comes next?
The formal data release is set for Saturday at the ESMO meeting — the key moment for the market to reassess.
This means → if the official figures match the leaked version, the sell-off may already be priced in; if additional detail improves the overall picture, there is room for a rebound.
Until then, the market sits in an information vacuum — no official confirmation, no official denial.
市场有风险，内容仅供研究参考，不构成投资建议。