Coronavirus cases in the U.S. double over three weeks

Covid-19 case numbers are on the rise again in the U.S., following months of significant decline.

New case figures have doubled per day over the past several weeks due primarily to the more contagious delta variant, as well as stalled vaccination rates across the country.

On Monday, confirmed infections climbed to an average of 23,600, doubling the June 23 figure, which was 11,300, according to Johns Hopkins University data.

 Case numbers have reportedly shot up in all states except South Dakota and Maine.

Despite the jump in the numbers, cases remain well below their peak of close to a quarter-million a day in January. And daily death rates remain thousands below the 3,400-plus Americans dying each day during the winter. 

Mississippi, the state with the lowest vaccination rate nationally, has experienced a 150% rise in hospitalizations over the past three weeks.

Louisiana's vaccination rate more than 15 percentage points below the national average of 55.6%., and authorities in New Orleans say they will likely extend virus-mitigation efforts at large venues for large gatherings. 

Dr. James Lawler, of the Global Center for Health Security at the University of Nebraska Medical Center in Omaha, told the Associated Press, "I think people have no clue what's about to hit us," when it comes to the delta variant. 

"The descriptions from regions of the world where the delta variant has taken hold and become the predominant virus are pictures of ICUs full of 30-year-olds," he said, adding that re-imposing mask mandates and limited gatherings may help curb the spread of the variant.