Traders work on the floor of The New York Stock Exchange.Spencer Platt/Getty Images The Dow industrials tumbled 905 points in a shortened session Friday. A new strain of coronavirus discovered in South Africa prompted travel restrictions worldwide. Scientists says the variant appears heavily mutated. US stocks closed sharply lower Friday as investors moved out of risk assets after rapidly rising cases of coronavirus from a new strain drove worries that the pandemic would throw the global economy off its course of recovery. Wall Street's key benchmarks had an ugly Black Friday, with the Dow Jones Industrial Average down by over 900 points in a shortened trading session.