CNN  — 

Last week, the number of Covid-19 cases in children in the US reached levels not seen since the winter surge. And with the return to schools, the Delta variant on the rise and this winter approaching, health officials are concerned it could get worse.

After a decline in early summer, child cases have increased exponentially – with more than a four-fold increase in the past month, according to the latest report from the American Academy of Pediatrics and the Children’s Hospital Association.

From about 38,000 cases a week near the end of July, the week ending August 19 saw more than 180,000 cases in children, the report said.

“The virus is raging in all these children who are unvaccinated, which is why in schools mask mandates are so important,” CNN medical analyst Dr. Jonathan Reiner told Jake Tapper, pointing out that people younger than 12 are not eligible to be vaccinated and inoculation rates are low among adolescents who are eligible. “They have no other protection. They’re literally sitting ducks.”

The rise has come while 48.3% of the population is not fully vaccinated, according to data from the Centers for Disease Control and Prevention – and as the daily average of newly reported cases has climbed to more than 151,000.

Health experts have been particularly concerned about cases among children as students return to school, many without mask mandates and without access to vaccines.

Pfizer/BioNTech’s vaccine was fully approved by the US Food and Drug Administration on Monday for Americans 16 and older, which National Institutes of Health Director Dr. Francis Collins told CNN was a “ray of sunshine in the midst of all these dark Covid clouds.”

The two companies said Wednesday they have begun to submit data, including that from a trial with 306 people, to the US Food and Drug Administration for approval of a booster dose of their Covid-19 vaccine.

Moderna announced it has completed its submission to the FDA for full approval of its Covid-19 vaccine for people 18 and older. Moderna said it has requested priority review from the agency. Moderna’s vaccine is currently available under emergency use authorization for people age 18 and older. The company began submitting data for approval to the FDA in June.

Still, children younger than 16 aren’t fully approved for a vaccine, and the emergency use authorizations in place only cover adolescents 12 and older.

Children ages 5 to 11 are the next group in line to become eligible to receive the Covid-19 vaccine, and an updated emergency use authorization from the FDA would make at least 28 million additional children – representing about 9% of the US population – eligible to receive the vaccine, according to a CNN analysis of federal data.

You asked, we’re answering: Your top questions about Covid-19 and vaccines

But the process of authorizing a vaccine for that age group may not be completed until the end of the year, US Surgeon General Dr. Vivek Murthy told CNN’s Brianna Keilar.

The timing is a problem, Dr. Paul Offit, a member of the FDA’s vaccines advisory committee, told CNN, because the more transmissible Delta variant is spreading and the cold dry weather of the winter months makes it easier for the virus to spread – all while children are sitting together in classrooms.

“You are going to have a group of fully susceptible people all in one place,” he told Jake Tapper. “That’s not a good recipe.”

And though it would be good to have vaccines for children before then, it is important for health officials to take their time in making sure the vaccines are tested heavily – and deemed safe.

“We’re moving as quickly as we can, it’s just not easy to move that quickly when you talk about doing big vaccine trials,” said Offit.

Hospitalizations surpass the six-figure mark

More than 100,000 people are hospitalized with Covid-19 in the US, the first time the country has surpassed that mark since January, according to data from the US Department of Health and Human Services.

Covid-19 hospitalizations have been on the rise in the US since early July. They’ve nearly tripled in the past month, and have grown by 10% in the past week alone. Current hospitalizations are about 71% of the peak from January 14, according to HHS data.

Florida and Texas account for nearly a third (31%) of current Covid-19 hospitalizations. Florida has the worst per capita hospitalization rate in the country – about 80 hospitalizations per 100,000 people – followed by Alabama, Mississippi, Georgia and Louisiana, each with more than 55 hospitalizations per 100,000 people.

Covid-19 hospitalization rates are still highest among seniors, but the gap is smaller than it was during the winter surge. In fact, Covid-19 hospitalization rates among children and adults under 50 are the highest they’ve ever been, CDC data shows.

An ensemble forecast published Wednesday by the CDC projects that new Covid-19 hospitalizations are likely to remain stable or have an uncertain trend over the next four weeks. It’s the first time since mid-July the forecast did not project an increasing level of hospitalizations.

Wednesday’s forecast predicts there will be 7,800 to 27,000 new confirmed Covid-19 hospital admissions likely reported on September 20. Since July 14, the forecasts had projected that hospitalizations would increase each week.

The forecast also predicts that new Covid-19 deaths will likely increase over the next four weeks, projecting a total of 651,000 to 680,000 deaths reported by September 18. The previous forecast, published August 18, predicted up to 664,000 Covid-19 deaths by September 11.

As with previous weeks, the agency says that its Covid-19 cases forecast should be interpreted with caution because actual numbers have fallen outside the range of previous predictions.

Schools take different approaches to rising cases

A boy receives a mandatory COVID-19 test at Northridge Middle School on August 11.

As cases rise among children, some school leaders are pressing for precautions while others are banning mask mandates.

Throughout Florida’s 15 largest school districts, at least 11,851 students and 2,610 employees have tested positive for Covid-19, amounting to more than 14,461 confirmed cases since the school districts started keeping track of cases for the 2021-22 school year, according to a CNN analysis.

Florida Gov. Ron DeSantis has issued an executive order banning schools from instituting mask mandates, but eight counties have defied the order as cases have grown.

South Carolina Gov. Henry McMaster also issued a ban on mask mandates, prompting a lawsuit from the American Civil Liberties Union, according to a complaint filed Tuesday.

“This is a disability rights issue,” said Susan Mizner, ACLU disability rights program director.

“Students with health conditions or disabilities that make them vulnerable to COVID have a right to attend school without endangering their health or safety. Schools who have children with these conditions have legal obligations under federal disability rights laws,” Mizner said in an ACLU statement.

McMaster’s spokesperson Brian Symmes declined to specifically comment on the lawsuit, but said, “The only truly inclusive option is to allow every parent to decide whether their child will wear a mask in school.”

On the other hand, the Los Angeles Unified School District has implemented strong mitigation measures and appears to have kept infection rates under 1% during the first week of classes.

The school district, the second-largest in the country, enacted the measures throughout its more than 1,000 schools.

Teachers and employees are required to be fully vaccinated by October 15. Masks are required for all students, staff and visitors. The district also has a “cohort” model in place, which aims to keep as many students in the same classroom and with the same group of students as often as possible.

A rigorous and costly testing initiative has also been put into place. Every student and employee must undergo free weekly testing regardless of vaccination status in order to be able to enter a school.

The Massachusetts Department of Elementary and Secondary Education has implemented a mask mandate in all public K-12 schools, effective immediately.

It applies to students 5 and older, teachers and staff, according to a news release from the education department.

The mandate is in full effect through October 1. After that date, middle and high school officials can lift the mandate for vaccinated students and staff, provided 80% of students and staff in a school building are vaccinated, the release says.

CNN’s Steve Almasy, Melissa Alonso, Jen Christensen, Jacqueline Howard, Virginia Langmaid, Deidre McPhillips, Michael Nedelman, Mallory Simon, Elizabeth Stuart, Naomi Thomas and Ben Tinker contributed to this report.