Moderna Tumbles 25% After Apparent Early Leak of Melanoma Vaccine Data; BioNTech Dips, Pfizer Edges Higher

A late-stage melanoma vaccine report that was posted online and quickly pulled is driving a violent repricing in Moderna (NASDAQ:MRNA | MRNA Price Prediction) shares, even though its findings looked favorable on their face. Moderna stock is at $184.87, down 25% this afternoon, a drop that reveals the elevated expectations built into the shares. Even after the slide, Moderna shares are up 526% year to date (YTD), a run that raised the bar for the full readout.

Merck (NYSE:MRK) is Moderna’s partner on the personalized vaccine, intismeran autogene, which pairs the shot with Merck’s immunotherapy Keytruda. Damage across the biotech group looks contained, with the iShares Biotechnology ETF (NASDAQ:IBB) down 2%. Broader-market selling is smaller, as the SPDR S&P 500 ETF Trust (NYSEARCA:SPY) is down 1.32%.

Retail sentiment toward Moderna stock has turned alongside the selloff. On WallStreetBets, Reddit chatter about the company registers as bearish, with a post titled “$MRNA is stupid” drawing the most engagement.

Briefly Posted Melanoma Results Spark Heavy Selling

Results from the late-stage trial briefly appeared online. The personalized melanoma vaccine Moderna is developing with Merck was posted on a medical news website shortly after midday on October 22 and taken down soon afterward. That posting came ahead of a scheduled presentation at the European Society for Medical Oncology (ESMO) Congress on October 24. According to the report, the vaccine combined with Keytruda lowered the risk of melanoma returning or death compared with the immunotherapy alone, and Moderna declined to comment.

In August, Moderna and Merck said the trial met its main goals without releasing detailed results. Earlier data pointed to a clear benefit. Five-year Phase 2b results presented at the American Society of Clinical Oncology (ASCO) meeting in 2026 showed a 49% reduction in the risk of recurrence or death with the combination versus Keytruda alone. Moderna has described the melanoma readout as an important pivotal catalyst, central to its push to build an oncology franchise beyond respiratory vaccines.

mRNA Rival BioNTech Slips While Pfizer Edges Up

Moderna and BioNTech (NASDAQ:BNTX) both build vaccines and cancer therapies on messenger RNA (mRNA) technology, while Pfizer (NYSE:PFE) is a diversified drugmaker. BioNTech stock is trading at $89.26, down 2%, a far smaller decline despite the shared platform. Meanwhile, Pfizer stock is at $30.11, up 0.9%, moving against the selloff in Moderna shares.

The leaked report pointed to a lower risk of recurrence or death, and the August statement from Moderna and Merck already confirmed the trial met its main goals. Skeptics counter that the enormous run in Moderna stock this year already reflected a great deal of optimism.

BioNTech and Pfizer are moving far less sharply, showing how specific the selling is to this readout, as BioNTech bulls point to its own personalized cancer pipeline, while bears flag shrinking COVID vaccine sales. Pfizer’s bull case rests on its diversified portfolio, though bears note declining COVID vaccine demand.

Autogene cevumeran, an individualized mRNA cancer immunotherapy in BioNTech’s pipeline, overlaps directly with the personalized approach Moderna and Merck are taking. For Pfizer, the clearest mRNA link is the Comirnaty COVID-19 vaccine developed with BioNTech. Every approved Moderna product is an infectious disease vaccine, making intismeran autogene central to its growth plans.

Moderna’s Melanoma Vaccine Data Faces Its ESMO Test

The next test is whether the full ESMO presentation backs up the favorable picture in the briefly posted report, and Merck has its own stake since Keytruda is the backbone of the combination regime.

Intismeran autogene is in nine Phase 2/3 trials across melanoma, non-small cell lung cancer, bladder cancer and renal cell carcinoma, giving that result read-through for Moderna’s wider oncology program. Investors weighing their exposure should size their MRNA stock positions carefully given how sharply the shares can swing on trial data.

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