A record surge in Moderna Inc.’s shares delivered a $5.5 billion blow to short sellers who had bet that the vaccine maker’s years-long slump would continue.
Moderna’s stock price soared 177% on Wednesday after the company said its personalized cancer vaccine developed with partner Merck & Co. helped reduce the recurrence of melanoma in a late-stage trial. The jump generated paper losses of about $5.5 billion for short sellers, bringing mark-to-market losses to roughly $7.7 billion this year, according to data from S3 Partners LLC.
“This is an exceptionally painful move for Moderna shorts,” said Matthew Unterman, managing director at S3 Partners. “Today’s move materially changes the risk/reward for anyone maintaining a bearish position.”
Moderna’s stock had been on a tear this year, gaining 114% even before the melanoma trial results, as investors piled into the firm on hopes that its flu vaccine would help the company diversify away from its declining Covid immunization business. Shares had suffered four straight years of losses as demand for its Covid shot waned, dragging the stock nearly 94% below its 2021 peak.
Wall Street analysts lauded the trial’s results as a huge potential boon for the firm. Needham analyst Joseph Stringer called the melanoma study a “landmark win” for Moderna, saying it could turn the firm’s oncology franchise into the next growth driver. Meanwhile, William Blair’s Myles Minter upgraded his rating to outperform from market perform, telling investors Moderna now has a clear line of sight to revenue diversification from its Covid business.
Losses for short sellers could have been even worse too. Short interest as a percentage of Moderna’s float, a measure of how many shares are available to be traded, had reached as high as 20% earlier this year before falling to about 14% as traders unwound some of the bearish bets, according to S3 Partners.
“What makes today more consequential is that the short trade had already been unwinding, roughly 20 million shares, or a quarter of positions have covered in 2026, so a move of this magnitude will force additional shorts to reassess or reduce positions,” Unterman said.
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