Moderna shares surged 176.97% to $174.38, marking the largest one-day gain for an S&P 500 stock this century, driven by positive late-stage results for its personalized mRNA cancer vaccine with Merck. The rally added $44B to its market cap, bringing it to $69.6B and making it the second-best performer in the index for the year. Despite the historic move, analyst Edmund Ingham maintained a Hold rating, citing the need for further clinical validation before full Phase 3 data release. Shares pulled back 14% in premarket trading Thursday as investors took profits.