S&P 500 Gains and Losses Today: Moderna Falls; Synopsys Stock Climbs on Nvidia Partnership

Synopsys was the best-performing stock in the S&P 500 Monday after announcing an expanded partnership with Nvidia. SOPA Images / LightRocket / Getty Images Close Key Takeaways A major vaccine producer came under pressure following a report federal health regulators plan to tighten vaccine approval rules. Meanwhile, an agreement with the world's most valuable company bolstered a software firm whose products help customers design and test semiconductors. Major U.S. equities indexes lost ground to start Decemb ...