In India where the Delta variant was first identified and caused a huge outbreak " cases have plunged over the past two months. A similar drop may now be underway in Britain. There is no clear explanation for these declines. In the U.S., cases started falling rapidly in early January. The decline began before vaccination was widespread and did not follow any evident changes in Americans' Covid attitudes. This spring, caseloads were not consistently higher in parts of the U.S. that had relaxed masking and social distancing measures (like Florida and Texas) than in regions that remained vigilant. Large parts of Africa and Asia still have not experienced outbreaks as big as those in Europe, North America and South America. How do we solve these mysteries? Michael Osterholm, who runs an infectious disease research center at the University of Minnesota, suggests that ... Americans should not assume that Delta is destined to cause months of rising caseloads. Nor should they assume that a sudden decline, if one starts this summer, fits a tidy narrative that attributes the turnaround to rising vaccination and mask wearing. We are certainly not powerless in the face of Covid. We can reduce its risks, just as we can reduce the risks from driving, biking, swimming and many other everyday activities. But we cannot eliminate them. "We're not in nearly as much control as we think are," Osterholm said.