Two-thirds of Americans in highly vaccinated counties now live in coronavirus hot spots, according to an analysis by The Washington Post, as outbreaks of the highly transmissible delta variant — once concentrated in poorly vaccinated pockets — ignite in more populated and immunized areas.

The Post analysis illustrates how rapidly the state of the pandemic changed in July from a problem for the unvaccinated to a nationwide concern.

The Post classified the highest top quarter of counties as high vaccination, with at least 54 percent of the population fully vaccinated. The lowest quarter of counties were classified as low vaccination, with fewer than 40 percent of the population fully vaccinated. The CDC identifies hot spots as areas with high and rising caseloads, as compared with areas with moderate or low covid-19 outbreaks.