Experts say the higher death toll is a result of a confluence of factors: most crucially lower-than-needed vaccination rates, but also the relaxation of everyday precautions, like masks and social distancing, and the rise of the highly contagious Delta variant.

Essentially, public health experts said, many Americans are behaving as though Covid-19 is now a manageable, endemic disease rather than a crisis — a transition that will happen eventually but has not happened yet.

Yet many are also refusing to get vaccinated in the numbers required to make that transition to what scientists call “endemicity,” which would mean the virus would still circulate at a lower level with periodic increases and decreases, but not spike in the devastating cycles that have characterized the pandemic. Just 59 percent of Americans are fully vaccinated, the lowest rate of any Group of 7 nation.