The highly contagious covid-19 delta variant is spreading like wildfire among children and teens, who accounted for 19 percent of reported U.S. cases in weekly data through July 29, the American Academy of Pediatrics (AAP) reported Tuesday.

Children’s Hospital New Orleans has not had an empty hospital bed in the intensive care unit for weeks, said Dr. Mark Kline, physician-in-chief at Children’s Hospital New Orleans, during a press conference Monday.

The AAP counted 71,726 new cases among children from July 22 to July 29 — a “substantial” increase from about 39,000 cases reported a week before, and five times as many kids who were sick at the end of June. For perspective, about 79,000 people in the U.S. of all ages tested positive in a week in late June.

The definition of a child varies by state but generally includes those up to age 17 or 18, CNN reported.

Children under the age of 12 are not eligible for any of the three vaccines available in the U.S. and the delta variant has put them especially at risk, health experts say.

As most of the U.S. prepares to go back to school, the idea that children are not vulnerable to covid-19 is being blown away. Close to 4.2 million children have tested positive for the virus since the pandemic began through July 29, 2021.

Louisiana has seen a surge in new cases among children. Of the 11,109 new covid cases recorded since Friday, July 30. children accounted for more than 2,000 of them, WWL-TV reported, citing the state’s Department of Health. That’s about 18 percent of new cases.

Among U.S. states reporting to the Academy of Pediatrics and the Children’s Hospital Association, 0.1 percent to 1.9 percent of all their child covid-19 cases resulted in hospitalization. Children were 0.00 percent to 0.26 percent of all covid-19 deaths, and seven states reported zero child deaths.

“I am as worried about our children today as I have ever been,” said Dr. Kline, physician-in-chief at Children’s Hospital New Orleans, during a press conference on Monday. “This virus, the delta variant of covid, is every infectious disease specialist’s and epidemiologist’s worst nightmare.”

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Louisiana Gov. John Bel Edwards reinstated the statewide mask mandate on Monday for Louisianans over the age of 5, regardless of vaccination status, Newsweek reported. Masks must be worn indoors statewide, including in schools, as of Aug. 4.

In Florida, Gov. Ron DeSantis downplayed the surging covid-19 cases that made the state the U.S. covid epicenter for weeks in a row, accounting for one in five new cases. DeSantis doubled down Tuesday on his promise not to impose a mask mandate, insisting that the spike is seasonal. He has threatened to withhold funds from school districts if they mandate masks for students. Some of Florida’s largest school districts challenged the governor, announcing that they will keep or issue new mask mandates.

“It’s important for everyone to know that we’re seeing sicker kids, we’re seeing more kids be admitted that are sick with actual covid illness, and that those kids, some of them are in our intensive care unit and some of them are intubated,” said Dr. Nick Hysmith at Le Bonheur Children’s Hospital in Memphis, Tennessee.