Why is Moderna stock sliding today?

Moderna shares are sliding 2.3% in morning trading today, extending a dramatic prior-session collapse driven by the premature disclosure of Phase 3 trial data for its personalized melanoma cancer vaccine, intismeran autogene, developed in partnership with Merck. The data, originally scheduled for formal presentation at the ESMO Congress in Madrid on Saturday, was published early by a medical news website on Thursday afternoon before being taken down, forcing Moderna and Merck to release the results officially.

The Phase 3 INTerpath-001 trial data were clinically encouraging — the vaccine-Keytruda combination reduced the risk of melanoma recurrence or death by 42% versus Keytruda alone across a study of over 1,100 patients. However, the result fell below the 49% risk reduction observed in an earlier Phase 2b study, and the manner of the disclosure rattled investors who had bid the stock up more than 500% year-to-date heading into the event. Analysts across Wall Street are weighing in today: Citi reiterated its Sell rating and questioned whether the vaccine’s benefit justifies the complexity of individualized tumor harvesting and manufacturing, while Bernstein maintained its Market Perform rating and characterized the selloff as a "sell the news event." Mizuho analyst Jared Holz called Moderna a "do-not-trade" stock for many investors given its extreme volatility, and BMO Capital Markets noted the plunge reflects the outsized expectations that had been baked into the stock’s enormous run.

The broader market is providing little support, with the S&P 500 off 0.4%, the Dow Jones down 1.1%, and the Nasdaq slipping 0.1% during today’s session. Sector peers are largely insulated from Moderna’s pain — Pfizer and BioNTech are each down less than 1%, and the broader biotech index is roughly flat, confirming the pressure is squarely Moderna-specific rather than a sector-wide phenomenon. Partner Merck is also modestly lower in sympathy.

The combination of a "sell-the-news" unwind after a historic rally, Phase 3 data that met — but did not exceed — elevated market expectations, and a wave of cautious analyst commentary published today has kept Moderna under pressure on Friday. The stock touched a session low of $183 before recovering partially to trade at $198, still well below its 52-week high of $254.48 reached just two sessions ago.