The U.S. has logged 40 million Covid-19 cases since the start of the pandemic, as the fourth wave brought on by the delta variant continues to spread.

The country has recorded 40,000,070 cases and 651,690 deaths, according to the latest NBC News tally. It recorded 35,355 news cases and 279 deaths Sunday. About 207 million people have received their first doses of a vaccine, and more than 175 million have been fully vaccinated.

Vaccination rates have risen slowly since July, but still no state or territory has passed the 70 percent fully vaccinated threshold, and the country is nowhere close to its peak in April, when more than 3 million people were getting shots every day.

Health care workers attend a patient with Covid-19 at the Cardiovascular Intensive Care Unit at Providence Cedars-Sinai Tarzana Medical Center in Tarzana, Calif., on Sept. 2, 2021. (Apu Gomes / AFP - Getty Images)

The fourth wave, which many experts say could have been prevented with better vaccination rates, has overwhelmed hospitals.

At Billings Clinic in Montana, the intensive care unit is nearing 150 percent capacity as the hospitals in the state have called on the National Guard for help.

Hospitals are seeing an average of 100,000 Covid patients a day, higher than at other any point since last winter, when the vaccines weren't available for most people. At the same time, hospitals face a nurse staffing crisis, as many nurses exhausted by the pandemic are quitting or retiring.

August was Florida's deadliest month for Covid cases since the pandemic began — it recorded more than 1,300 deaths as hospitalizations among children skyrocket.

In central Texas, a school district closed until after Labor Day after two teachers died of Covid./agencies