Moderna’s stock surged 177% on Wednesday after the company disclosed positive late-stage trial results for its personalized cancer vaccine, administered in partnership with Merck & Co. The gain inflicted approximately $5.5 billion in losses on short sellers, bringing their total losses for the year to roughly $7.7 billion, according to S3 Partners data.
The Moderna shares had been a favored target for short sellers, with the short interest peaking near 20% of the float at the start of the year. That exposure has since declined to about 14% as some traders closed out bearish positions ahead of the rally. Analysts welcomed the development as a potential inflection point for the company, which had endured four consecutive years of losses and saw its stock fall nearly 94% from its 2021 peak amid waning demand for COVID-19 vaccines.
Wall Street upgraded its outlook for Moderna following the trial results. Needham’s Joseph Stringer called the cancer vaccine data a “milestone victory” that could position oncology as the next growth engine. William Blair’s Myles Minter raised the stock rating to “Outperform,” citing clearer revenue diversification prospects beyond its coronavirus products.
Short sellers had already begun reducing exposure before Wednesday’s surge. S3 Partners noted that roughly 20 million shares, or a quarter of the outstanding short positions, had been covered in 2026, a move that may force further position unwinding. Analysts suggested this dynamic could lead to additional upward pressure on Moderna’s shares in the near term, potentially extending gains into Thursday or Friday.
