WASHINGTON/LONDON—Shares tumbled on Wall Street on Friday as they reopened after Thanksgiving, while European stocks saw their biggest sell-off in 17 months and oil prices plunged by $10 per barrel as fears over a new coronavirus variant sent investors scurrying to safe-haven assets. The World Health Organization (WHO) on Friday designated a new COVID-19 variant detected in South Africa with a large number of mutations as being “of concern,” the fifth variant to be given the designation. Unofficially, the Dow Jones Industrial Average closed down 2.53 percent at 34,899.34 in its largest percentage drop in more than a year. The S&P 500 lost 2.27 percent, its worst one-day drop since Feb. 25, and the Nasdaq Composite dropped 2.23 percent, the biggest one-day route in two months. U.S. markets closed early on Friday after being shut all day on Thursday for the Thanksgiving holiday. The benchmark STOXX 600 index ended 3.7 …