Moderna Erases $18 Billion in Market Value the Day After Its Historic 177% Cancer Vaccine Surge

Moderna shares fell as much as 25% on Thursday, wiping out roughly $18 billion in market value, one day after the stock posted a 177% gain, its best single session ever, on breakthrough Phase 3 data for its personalized mRNA cancer vaccine intismeran. The drug, developed in partnership with Merck, was tested in combination with Merck's blockbuster Keytruda in more than 1,100 patients with high-risk melanoma that had been surgically removed. The combination demonstrated a clinically meaningful improvement in keeping patients cancer-free compared with Keytruda alone, with trial principal investigator Georgina Long calling it a landmark moment for adjuvant melanoma treatment.

Moderna closed Wednesday at $174.38, up from roughly $63 before the announcement, but by midday Thursday had retreated to around $130 to $142 as investors locked in gains. BioNTech fell roughly 4% in sympathy. Merck, which had climbed on the news, received a stock downgrade on Thursday.

JPMorgan analyst Jessica Fye cautioned that while intismeran's launch in adjuvant melanoma is key to Moderna returning to profitability, success in that indication was already priced into her model at an 85% probability of success, making the original run-up appear overdone. A separate Benzinga analyst note framed intismeran's long-term oncology potential as comparable to Keytruda's franchise-defining role for Merck. Moderna's trading volume on Wednesday reached 185 million shares, approximately 1,819% above its three-month average.