The S&P 500 lost nearly 34 percent during the COVID-19 crash from its February 2020 peak to its March 2020 low.
The index reached a record closing high on February 19, 2020. As the novel coronavirus spread internationally, governments introduced travel restrictions, business closures, and other measures that sharply reduced economic activity. Investors also reacted to uncertainty about corporate earnings, supply chains, and the speed of any recovery.
The S&P 500 reached its bear-market low on March 23, 2020, after an unusually rapid decline. The Federal Reserve cut interest rates, restarted large asset-purchase programs, and introduced emergency lending facilities. Governments also approved major fiscal support. These measures, together with changing expectations about vaccines and reopening, helped markets rebound.
The S&P 500 is an index of large U.S. companies, not a single stock or a worldwide market. The Dow and Nasdaq also fell sharply, but they measure different groups of companies and use different weighting methods.