Moderna Stock Falls 8% After Melanoma Vaccine Data Leak

Moderna (MRNA) shares fell another 8% on Monday after leaked melanoma vaccine data showed a 42% cut in recurrence or death risk, extending a selloff in biotech cancer stocks.

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What Happened to Moderna Stock?

Moderna stock fell 17.6% on Thursday to close at $202.63, after trading as much as 26% lower during the session. It slipped a further 1.25% on Friday to $200.10. Thursday's drop erased about $17 billion in market value and left the company valued near $81 billion.

The trigger was a posting on a medical news site around midday Thursday. It carried figures from the INTerpath-001 trial that were embargoed for a late-breaking presentation at the European Society for Medical Oncology congress in Madrid on Saturday. The page was removed within hours, but the numbers had already spread. Merck, which shares the program's costs and profits equally with Moderna, fell 1.76% that day.

What Do the Leaked Melanoma Vaccine Results Show?

The trial showed that intismeran combined with Merck's Keytruda cut the risk of recurrence or death by 42% (hazard ratio 0.58) compared with Keytruda alone. It enrolled 1,137 patients with stage IIB to IV melanoma. At about two years, 82.2% of patients on the combination were free of recurrence, against 70.0% on Keytruda alone. The combination also lowered the risk of distant spread or death by 38%.

The two arms performed identically in the first six months of treatment, with a hazard ratio of 0.99. After six months, a prespecified analysis showed a 58% reduction in risk, which points to a benefit that builds over time. Overall survival data remains immature, and the companies describe the trend only as favorable.

Why Did Investors Sell a Positive Result?

Investors sold because the 42% reduction came in below the 49% benefit seen in the earlier, smaller Phase 2b study, which had set the bar for the stock. The two trials enrolled different patients, so the figures are not a like-for-like comparison. The August announcement that the Phase 3 trial had met its primary endpoint had already driven a record rally. By October, much of the expected success was priced in, and a result at the low end of the 40% to 50% range triggered a classic sell-the-news reaction.

Sector Reaction and Strategic Context

The move rippled through related names. BioNTech fell about 3% on Monday, while Pfizer held steady. The sharp swing in a single large-cap name also matters for the biotech ETF category, where Moderna ranks among the more volatile holdings.

Intismeran is among the most advanced individualized cancer therapies. Each dose is built from a patient's own tumor mutations. A confirmed benefit in a Phase 3 trial would open a new commercial category for messenger RNA technology as demand for Covid-19 vaccines declines. Moderna and Merck say they are engaging with regulators on a path to approval.

Outlook

Moderna remains up several hundred percent this year despite roughly 25% lost since the Wednesday close. The full ESMO presentation and maturing survival data are the next tests of whether the post-six-month benefit holds. Trading in the shares is likely to stay volatile until those results are digested.