mRNA Vaccine Stocks Rise on Moderna-Merck Success -- WSJ

By Alex Janin

Drug company stocks soared following news that Moderna and Merck's experimental mRNA-based cancer vaccine succeeded in a late-stage trial at preventing melanoma from returning or spreading.

-- The S&P health-care sector is on track for an all-time closing high, as is Merck, according to data that goes back to 1972.

-- As of Wednesday afternoon, Moderna's stock had more than doubled, something that a member of the S&P 500 hasn't done in a single day since 2008, according to Dow Jones Market Data.

-- Merck's stock was up about 12%, on pace for its largest increase since 2009.

Moderna already had a significant contingent of investors betting against the stock. Roughly 13.7% of its publicly tradable shares were sold short. Sudden good news for companies in this circumstance can trigger a "short squeeze," wherein short sellers buy back stock to moderate losses, driving the share price up.

Broader excitement also rippled through to other companies developing similar types of drugs. German biotech company BioNTech, which helped pioneer the development of mRNA technology and is developing vaccines targeting colorectal and pancreatic cancers, is trading about 20% higher. Roche, which owns Genentech, BioNTech's partner on personalized cancer vaccines, was up 1.8%. French biotech Transgene, which is developing a different type of personalized cancer vaccine using a viral vector rather than mRNA, was up 15%.

"The stocks are reacting like you're going to use this vaccine after every surgery in cancer, and I think that's a massive overreach," Leerink Partners analyst Daina Graybosch said.

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August 19, 2026 14:29 ET (18:29 GMT)