The omicron variant of Covid-19, first identified in South Africa, has now been detected in countries from the U.S. to South Korea, underscoring the difficulties of curtailing contagious new strains.
Most infections stem from travelers carrying the disease across borders. Israel, for instance, said a confirmed case who arrived from Malawi rode on a bus from Tel Aviv. Italy’s first case traveled around the country for days before testing positive. The first omicron case was confirmed in the U.S. in a person who returned from South Africa, the Centers for Disease Control and Prevention said.