Moderna (NASDAQ:MRNA | MRNA Price Prediction) shares have crashed 20% as of 12:00 PM ET on Thursday after delivering one of the biotech sector’s most extraordinary single-day moves of 2026. CNBC co-anchor Andrew Ross Sorkin told viewers that Moderna’s Phase 3 results for its experimental cancer vaccine sent the stock soaring 177% on Wednesday, while partner Merck (NYSE:MRK) rallied 12.5%.
As Sorkin summarized on air, “The mRNA based shot, in combination with Merck’s immunotherapy called Keytruda, met key goals in a trial of patients with higher risk or advanced melanoma whose detectable cancer had been removed.“
Moderna Crashed 20% After Exploding 177%
The scale of Wednesday’s 177% move for Moderna reflects the commercial optionality investors assign to a working mRNA cancer vaccine platform. Moderna entered the news cycle carrying serious pipeline overhangs, including a $950 million litigation settlement paid in July 2026 and a norovirus program that did not meet statistical criteria for early success at a Phase 3 interim analysis. However, a validated oncology franchise changes that story.
Now, the stock is down 20% on Thursday, as it appears investors are taking profits and reconsidering how impactful this potential cancer vaccine would be for the business. MRNA’s one-week performance sits at 117.31%, and year-to-date at 369.03%.
The Personalized Cancer Vaccine Behind the Rally
The vaccine, known as intismeran autogene (mRNA-4157), is an individualized neoantigen therapy. In the five-year Phase 2b KEYNOTE-942 adjuvant melanoma readout presented at ASCO 2026, intismeran plus KEYTRUDA delivered a 49% reduction in risk of recurrence or death versus KEYTRUDA alone. Moderna disclosed on its Q2 2026 call that the Phase 3 adjuvant melanoma study is fully enrolled, with the interim analysis expected in the second half of 2026.
Moderna CEO Stéphane Bancel framed the setup in the company’s Q2 2026 press release in late July, saying Moderna would “continue to anticipate important pivotal readouts for our intismeran in melanoma and propionic acidemia programs.” Management has said nine Phase 2 and Phase 3 studies are underway across melanoma, NSCLC, bladder cancer, and renal cell carcinoma.
Why This Could Extend Merck’s KEYTRUDA Franchise
KEYTRUDA is Merck’s largest product and its most exposed asset heading into loss of exclusivity. Q2 2026 KEYTRUDA family sales reached $8.4 billion, up 4%. CEO Rob Davis has argued the loss of exclusivity transition is “more of a hill than a cliff,” with a “shallow dip with a fast return back to growth.”
An approved adjuvant melanoma combination would extend the franchise’s clinical utility into earlier lines of therapy.
The Biggest Risks After Moderna’s 20% Drop
Moderna’s historic rally reflects the possibility that its mRNA platform can become much more than a respiratory-vaccine business. A successful melanoma launch could create an entirely new oncology franchise for Moderna while strengthening Merck’s KEYTRUDA portfolio ahead of its patent expiration.
The upside is enormous, but with Thursday’s 20% drop, it appears shares are coming back down to Earth a bit after the 1-day 177% rally on Wednesday. Investors are already paying for a great deal of clinical and commercial success before approval has arrived.
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