The three major U.S. stock indices closed significantly lower on Monday, marking a sharp reversal from last week's gains. The S&P 500 suffered the steepest decline, falling by 2.95%, while the Nasdaq 100 and Dow Jones Industrial Average lost 3.56% and 2.58%, respectively. The sell-off was triggered by concerns over rising COVID-19 cases in several states, as well as worries about the economic impact of the ongoing Russia-Ukraine conflict. Investors also remained cautious ahead of key earnings reports from major tech companies later this week. The S&P 500 closed at 4,058.12, the Nasdaq 100 at 12,049.84, and the Dow Jones Industrial Average at 32,816.92. The sharp decline on Monday ended a rally that had seen the major indices reach record highs earlier this year. The S&P 500 had risen by more than 20% in 2022, while the Nasdaq 100 had gained over 30%.