Archive · 20 Aug 2026
Moderna’s Cancer Vaccine Surge Inflicts Billions in Short-Seller Losses
Moderna makes vaccines and medicines.
Its stock price rose sharply after a cancer vaccine showed encouraging results in a melanoma study.
The vaccine was developed with Merck.
Investors thought the results could help Moderna grow beyond its declining Covid vaccine business.
People who had bet that Moderna’s stock would fall lost a lot of money on paper.
Their losses from the stock’s rise were estimated at $5.5 billion in one day.
Analysts became more optimistic about Moderna’s future.
Some short sellers may now reduce or end their bets against the company.
Moderna shares jumped 177% after positive late-stage melanoma vaccine trial results.
The personalized cancer vaccine, developed with Merck, reduced melanoma recurrence in the trial.
Short sellers suffered estimated paper losses of $5.5 billion on Wednesday.
Their mark-to-market losses for the year reached approximately $7.7 billion.
Analysts said the results could make oncology Moderna’s next major growth driver.
- Who
- Moderna, Merck, investors, analysts, and short sellers.
- What
- Moderna shares surged 177% after a personalized cancer vaccine reduced melanoma recurrence in a late-stage trial.
- When
- On Wednesday; the article also reports year-to-date 2026 short-seller losses.
- Where
- The articles do not specify a location.
- Why
- Investors reacted to the melanoma trial results and the possibility that Moderna’s oncology business could diversify revenue beyond Covid vaccines.
Bullish analysts and investors
Bearish short sellers
Moderna’s future growth
Bullish analysts and investors
Analysts described the melanoma results as a potential landmark and said oncology could become Moderna’s next growth driver.
Bearish short sellers
Short sellers had bet that Moderna’s years-long stock slump would continue, reflecting a bearish view of its prospects.
Revenue diversification
Bullish analysts and investors
William Blair analyst Myles Minter said Moderna now had a clear path toward diversifying revenue beyond its Covid business.
Bearish short sellers
The company’s declining Covid immunization demand had contributed to its previous stock losses, supporting the rationale for bearish positions.
Position risk
Bullish analysts and investors
The share-price surge strengthened the case for investors expecting further gains and materially changed the risk-reward balance for short positions.
Bearish short sellers
Short sellers faced major losses and may reassess or reduce positions, although some had already covered roughly 20 million shares.
- Share-price move
- Moderna stock rose 177% on Wednesday.
- Short-seller loss
- Estimated paper losses were about $5.5 billion on Wednesday.
- Year-to-date losses
- Short sellers’ mark-to-market losses reached roughly $7.7 billion.
- Trial result
- Moderna and Merck’s personalized cancer vaccine reduced melanoma recurrence in a late-stage trial.
- Earlier stock performance
- The stock had gained 114% in 2026 before the trial announcement.
- Historical decline
- Shares remained nearly 94% below their 2021 peak after four straight years of losses.
- Short interest
- Short interest had reached about 20% of the float earlier in the year before falling to approximately 14%.