Moderna shares jumped 177 percent on Wednesday after the company reported positive late-stage data for a personalized melanoma vaccine developed with Merck, handing short sellers roughly $5.5 billion in mark-to-market losses for the session and pushing year-to-date losses to about $7.7 billion, according to S3 Partners data.
The trade that soured
Bearish bets against the vaccine maker had already been shrinking. Short interest as a share of the float peaked near 20 percent earlier this year before sliding to roughly 14 percent as traders covered about 20 million shares, roughly a quarter of outstanding short positions, over the course of 2026. Wednesday’s move now threatens to accelerate that exit. “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.”
Context behind the rally
The stock had climbed 114 percent before the trial readout, driven by optimism that a flu candidate could finally diversify revenue away from a Covid franchise that has evaporated. Shares had posted four consecutive annual declines, leaving them nearly 94 percent below the 2021 high. The melanoma data now offers a second potential pillar beyond respiratory vaccines.
Analyst reaction
Needham’s Joseph Stringer called the study a “landmark win” that could turn oncology into the next growth engine. William Blair’s Myles Minter upgraded the stock to outperform from market perform, arguing the company now has a credible path to revenue diversification from its Covid business.