CNN  — 

Covid-19 infections have continued to increase “exponentially” among children across the US, and now account for nearly 26% of all cases reported nationwide, according to data published Monday.

Over the past week, the American Academy of Pediatrics reported the second highest total of new diagnoses among children over the course of the pandemic, with 225,978.

That is a slight decline from the week before, when 243,373 new cases were reported.

The rise in cases comes as many students return to classrooms while not yet eligible for Covid-19 vaccines. Studies are underway for younger children, but currently only children 12 and older can get inoculated.

Health experts and officials have expressed concern about keeping young students safe until a vaccine is authorized for them.

“After declining in early summer, child cases have increased exponentially, with over 925,000 cases in the past four weeks,” AAP said in a statement.

Children still less likely to suffer serious disease

The weekly case number reported Monday is about a 215% increase in cases among children since the week of July 22-29 when the group counted 71,726 cases.

As of September 16, more than 5.5 million kids have tested positive for Covid-19.

Still, children are far less likely than adults to suffer serious disease or to die from Covid-19. Among states that report hospitalizations by age, children make up between 1.6% and 4.2% of patients hospitalized for Covid-19.

Among the states that report death by age, children accounted for no more than 0.25% of the deaths. Seven states have reported no pediatric deaths.

As of Sunday, the US Centers for Disease Control and Prevention reported 548 children younger than 18 had died for Covid-19 in the United States.

Jonathan Pagliarulo, 11, gets tested for Covid-19, after vaccinated family members tested positive for the virus.

Vaccines could be ready by the end of the year

Health experts, like CDC Director Dr. Rochelle Walensky, have said that public health agencies are working to have a vaccine ready for younger children by the end of the year.

According to Dr. Scott Gottlieb, a board member at Pfizer and the former commissioner of the Food and Drug Administration, that timeline could be as soon as Halloween.