The Delta Variant: What Scientists Know

The variant is gaining traction worldwide. But vaccines are driving down coronavirus case numbers in the U.S., and it’s unclear whether Delta will reverse that trend.

The super-contagious Delta variant of the coronavirus is now responsible for about one in every five Covid-19 cases in the United States, and its prevalence has doubled in the last two weeks, heath officials said on Tuesday. First identified in India, Delta is one of several “variants of concern,” as designated by the Centers for Disease Control and Prevention and the World Health Organization. It has spread rapidly through India and Britain. Its appearance in the United States is not surprising. And with vaccinations ticking up and Covid-19 case numbers falling, it’s unclear how much of a problem Delta will cause here. Still, its swift rise has prompted concerns that it might jeopardize the nation’s progress in beating back the pandemic.