The recent rise in Covid-19 cases in the U.S. has largely been driven by a handful of states, many of them the same places that first emerged as hot spots a year ago. Through Monday, about 75% of the previous week’s new cases in the U.S. came from Michigan, Florida, New York, Pennsylvania and New Jersey.

Covid-19 cases and the rate of new cases per 100,000 people are resurging in several states that, for long stretches, had kept the pathogen relatively at bay. Outside of the period from Thanksgiving to New Year’s, Michigan, Pennsylvania and New Jersey haven’t seen levels this high during the pandemic. And outside of that same holiday period, New York hasn’t had this many new cases since spring, and Florida not since the summer.

Public-health officials and epidemiologists say the increasing caseloads in many parts of the country can be attributed to a constellation of factors, including the spread of more transmissible variants; a rise in infections among younger, often unvaccinated, people; relaxed prevention efforts and loosened restrictions on indoor dining and masking; as well as pandemic fatigue.


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