Moderna’s stock surged 177% on August 19, 2026, after the company announced that its personalized cancer vaccine combined with Merck’s immunotherapy significantly reduced melanoma recurrence in a late-stage trial involving more than 1,100 patients [1, 2, 3]. The vaccine uses mRNA technology tailored to each patient’s tumor DNA with up to 34 tumor-specific targets, cutting the risk of recurrence by approximately 50% over five years of follow-up [3].
The trial results were hailed as "very interesting" and providing "real hope" by French oncologist Suzette Delaloge, who noted the vaccine was feasible for about 85% of participants [3]. Bank of America analyst Alec Stranahan called the findings a "watershed moment" for Moderna, opening a growth avenue beyond infectious diseases [2].
The sharp stock gain inflicted roughly $5.5 billion in losses on short sellers that day, adding to about $7.7 billion in mark-to-market short seller losses earlier in 2026, according to Managing Director Matthew Unterman of S3 Partners, who said the move "materially changes the risk/reward for anyone maintaining a bearish position" [1].
However, Moderna shares retreated about 25% on August 20, wiping out more than $18 billion in market value and bringing the company’s valuation down to roughly $51.5 billion from $69.6 billion before the drop [2]. This pullback came after investors took profits following the initial surge.
Moderna’s stock had previously struggled, down nearly 94% from its 2021 peak after Covid-19 vaccine demand waned, before rallying dramatically in 2026 due to the new melanoma vaccine news [1]. Co-founders Thomas Langer and Noubar Afeyan, along with CEO Stéphane Bancel, saw their net worths rise sharply on August 19 before falling again with the stock decline the next day [2].
The positive final data on the personalized cancer vaccine will be presented at upcoming medical conferences and submitted to regulatory authorities for review, as Moderna pushes to build momentum in oncology after its initial infectious disease successes [3].
