Moderna Soars as Vaccine-Drug Combo Slows Recurrence of Melanoma

It has been roughly 18 years since a stock on the S&P 500 more than doubled in a single day. Reset the clock to zero.

Shares in Moderna surged, not-a-typo, 176.97% on Wednesday after the biotech company and partner Merck said an experimental vaccine-drug treatment showed signs of slowing the recurrence of skin cancer. A bit of caution and celebration, analysts said, are in order. 

A Tale of Two Analysts

Moderna and Merck announced that their treatment, which combines jointly produced mRNA-based vaccine Intismeran with Merck’s immunotherapy drug Keytruda, slowed the return of melanoma and its spread to other parts of the body. The development, they said, is a result of a late-stage trial which enrolled more than 1,100 patients who already had their cancer surgically removed. But the companies have yet to publish their findings in a peer-reviewed setting. Instead, they pledged to present the trial data on the vaccine-drug combo at an upcoming international medical meeting and share it with regulators. 

From a pure medical standpoint, it represents a potentially triumphant breakthrough: Melanoma accounts for just 1% of US skin cancer cases, but is responsible for the vast majority of skin cancer deaths, according to the American Cancer Society. It would also break new ground for mRNA vaccines, which were first approved for public use during the COVID-19 pandemic. Moderna, which has suffered steep revenue declines and losses since making record earnings from its Covid shots, won FDA approval for the first mRNA-based flu shot earlier this month. For Merck, which rose 12.6% on Wednesday, the news represents new potential for Keytruda, a blockbuster drug that made $8.4 billion in second-quarter sales, or more than half the company’s $16.6 billion revenue. For investors, some analysts advised a chill pill while others said roll with it:

• “We think that retail investors should keep expectations measured,” said eToro analyst Lale Akoner. “The companies have not yet released the full trial data, overall survival results are still pending, and manufacturing personalized vaccines at scale could be expensive and complex.”
• RBC’s Trung Huynh estimated the new treatment could be worth up to $2.5 billion, adding: “We expect a significant ‘halo effect’ across the robust [cancer] program.”

Other biotech companies developing mRNA-based cancer therapies benefited from spillover sentiment on Wednesday. Germany’s BioNTech closed up 20.7% and Switzerland’s Roche up 4.6%.

Falling Short: Short sellers who bet Moderna’s extended slump would keep on slumping had a rough day. According to ORTEX, it’s one of the most shorted large-cap stocks on the market, with short interest amounting to 13.5%. Shorts, already reeling from Moderna rising more than 100% in 2026 prior to Wednesday because of its mRNA flu vaccine, were faced with paper losses of roughly $4.8 billion on Wednesday.