A covid variant first found in the U.K. is infecting Americans at a pace that far outstrips the original strain, which arrived in the spring. In the 43 days since B.1.1.7 was first found in the U.S., more than 900 cases have been reported. At around the same point, the first strain had infected only 165 people, though testing capacity was significantly weaker. … As of Tuesday, there were 932 reported cases of the U.K. variant among 34 states, according to data from the CDC.