The US remains among nations with the highest rate of new Covid-19 cases, driven mostly by a surge in the South, where many states are lagging in getting people vaccinated against the coronavirus.

"This is starting to look really ominous in the South. ... If you look at rates of transmission in Florida and Louisiana, they're actually probably the highest in the world," Dr. Peter Hotez, the dean of the National School of Tropical Medicine at Baylor College of Medicine, told CNN's Anderson Cooper on Friday.

Infection rates began to plummet in the US in the spring as vaccines became widely available, while the seven-day moving average of daily confirmed cases climbed in other nations, including India and Brazil, according to data from Johns Hopkins University.

In the month of August, the US has so far reported more than 1.5 million new cases of Covid-19, more than three times the numbers for Iran and India -- which now hold second and third place, JHU data shows. And the seven-day average has topped more than 135,000 cases, well ahead of other nations.