U.S. stocks fell aggressively on Monday amid fears that a rebound in Covid-19 cases would slow global economic growth. Sales rose as the session progressed and the Dow Jones Industrial average was now heading for its biggest decline of the year.

The Dow lost 777 points, or 2.2%, outperforming a 2% decline in late January. The S&P 500 lost 1.9%, with the energy and industrial sectors being the worst performers. The Nasdaq Composite lost 1.6%.

US 10-year Treasury yields fell to a new five-month low of 1.19%, adding to fears about the weakening economy. Crude oil fell 5%.

“Two concerns come together this morning: technical concerns and growth concerns,” said Mohamed El-Erian, Allianz chief financial advisor and former PIMCO CEO, in CNBC’s “Squawk Box” on Monday. “That’s what all asset classes tell you this morning.”

Covid cases have rebounded in the US this month, with the Delta variant spreading among the unvaccinated. The U.S. is seeing an average of nearly 30,000 new cases per day for the last seven days through Friday, up from a seven-day average of around 11,000 cases per day a month ago, according to CDC data. Cases have flared up around the world because of the delta variant.

United and American Airlines shares lost more than 7%. Delta fell 6%. Along with stocks in cruise lines and airlines, major stocks related to the global economy fell. Boeing and General Motors each lost more than 5%. Caterpillar lost 3%.

“The market seems poised to take on a more defensive character as we see a significant slowdown in earnings and economic growth,” Morgan Stanley’s US equity strategist Mike Wilson wrote in a statement on Monday. “Market breadth has been deteriorating for months and, in our view, is just another confirmation of the mid-cycle transition. It usually ends with a significant (10-20%) index correction.”

Wilson is advising customers to buy staples like Mondelez International to help weather the decline.

Oil prices fell on fears of a slowdown in growth and as OPEC + agreed to begin phasing out production cuts. Energy stocks were among the worst performers in the market, with ConocoPhillips down more than 3%. Exxon Mobil lost 3%. WTI crude oil lost 6% to about $ 68.12 a barrel.

Banks took a hit as yields fell, hurting their prospects for profitability. JPMorgan and Bank of America lost about 2.5% each.

Big tech stocks weren’t immune to the sell-off, with Apple and Alphabet each falling more than 2%.

However, some defensive stocks rose amid the market sell-off. Walmart and Procter & Gamble shares have traded in the green along with many utility companies.

Despite the decline on Monday, the overall damage for the market remains small. The S&P 500 is still only 3% below its record last week and investors are hoping the better-than-expected earnings results will break the market.

A busy week of profits is ahead, with nine Dow components to report and 76 S&P companies to provide quarterly updates. United Airlines and American Airlines will report as well as the social media companies Snap and Twitter. CSX, Johnson & Johnson, Coca-Cola, Honeywell, IBM, Intel and Netflix are also on the program.

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