Moderna Stock Crashes 25% After Cancer Vaccine Data Leak Wipes Out $24 Billion

Moderna shares collapsed on Thursday — falling as much as 25% and wiping out roughly $24 billion in market value — after late-stage trial data for its personalized cancer vaccine, developed with Merck, leaked ahead of schedule. The stock was the worst performer in the S&P 500, closing around 18–25% lower depending on the session's measure, in what analysts described as a brutal "sell-the-news" reaction after a months-long rally.

Key Facts

• Moderna (MRNA): down ~18% at the close; intraday drop exceeded 25%
• Roughly $24 billion of market value erased in one session
• Cause: leaked late-stage data for the personalized melanoma (skin cancer) vaccine co-developed with Merck
• The fall came after a months-long surge in the stock — expectations were sky-high
• MRNA was the single worst-performing stock in the S&P 500 on Thursday

What exactly happened?

Moderna's personalized cancer vaccine — a treatment tailored to each patient's tumor, built on the same mRNA platform as its COVID shots — is the company's most important pipeline hope beyond respiratory vaccines. When late-stage melanoma trial data surfaced through a leak rather than a controlled announcement, traders reacted instantly and brutally. After a long run-up had priced in near-perfect results, even data that might look reasonable in isolation was treated as a disappointment: the classic setup for a "sell-the-news" collapse.

Why does one leak move a stock this much?

Because for Moderna, this vaccine is not one product among many — it is the story. The company's COVID revenue has faded, and investors have been paying for the promise that mRNA can be turned into personalized cancer treatment. A leak removes management's ability to frame the data, and in a market already dumping risk — Thursday's Nasdaq fell 2.6% — a biotech name with sky-high expectations had no cushion at all.

What happens next?

All eyes turn to the full official data release and any statement from Moderna and Merck. If the complete results are stronger than the leaked fragments suggested, some of Thursday's loss could reverse; if they confirm investor fears, the stock's re-rating may have further to run. Either way, volatility is guaranteed — this is now one of the most closely watched biotech stories in the market.

FAQ

What is a personalized cancer vaccine?
A treatment made for one patient: scientists sequence the patient's tumor, identify its unique mutations, and build an mRNA vaccine that trains the immune system to attack exactly those cells.

Who is Moderna's partner on the vaccine?
Merck (known as MSD outside the U.S. and Canada), which co-develops the therapy and markets the cancer drug Keytruda, with which the vaccine is being tested.