More Contagious Virus Variant Is Now Dominant in U.S., C.D.C. Chief Says

The B.1.1.7 variant, first identified in Britain, is now the source of most new coronavirus infections in the United States, the director of the Centers for Disease Control and Prevention said.

WASHINGTON — A highly infectious variant of the coronavirus that was first identified in Britain has become the most common source of new infections in the United States, the director of the Centers for Disease Control and Prevention said on Wednesday. The worrisome development comes as officials and scientists warn of a possible fourth surge of infections. Federal health officials said in January that the B.1.1.7 variant, which began surging in Britain in December and has since slammed Europe, could become the dominant source of coronavirus infections in the United States, leading to a huge increase in cases and deaths. At that point, new cases, hospitalizations and deaths were at an all-time high. From that peak, the numbers all declined until late February, according to a New York Times database. After several weeks at a plateau, new cases and hospitalizations are increasing again. The average number of new cases in the country has reached nearly 65,000 a day as of Tuesday, concentrated mostly in metro areas in Michigan as well as in the New York City region. That is an increase of 19 percent compared with the figure two weeks ago.