(CNN) Inside one children's hospital in Chicago, Covid-19 cases are roughly three times higher than the hospital's previous peak in December 2020. In the past week, hospitalizations are four times higher what the hospital typically sees.
And while the number of children going into the intensive care unit at the Ann & Robert H. Lurie Children's Hospital of Chicago has not increased, Dr. Larry Kociolek says he expects that to change if infection numbers keep climbing.
But so far, among all the young patients admitted to the hospital recently, only one was fully vaccinated, said Kociolek, a pediatric infectious disease physician. That child had multiple underlying conditions that put them at risk for severe illness, he said.
"I think we're definitely seeing the impact of vaccines in kids older than 5. The kids that are hospitalized are essentially all unvaccinated," Kociolek said. He added that many of the infections the hospital is treating are mild or were incidentally caught during the hospital's screening process in children who were getting admitted for something else.
Hospitals across the country are seeing a similar surge in pediatric patients -- including children who are too young to be vaccinated -- as overall infection numbers rapidly climb, fueled by contagious variants and holiday gatherings.
An average of 305 children were admitted to hospitals with Covid-19 on any given day over the week that ended on December 26, according to data from the US Centers for Disease Control and Prevention and the US Department of Health and Human Services. That's more than a 48% increase from the previous week and just about 10% lower than the peak average of 342 children admitted to hospitals, a number that was recorded in late August and early September.
Roughly two-thirds of their cases and half of hospitalizations are among children who are younger than 5 and not yet eligible for a Covid-19 vaccine, Kociolek told CNN's Jake Tapper on Tuesday afternoon. But many who are eligible have still not gotten their shots.
"In Chicago, about 70% of children between age 5 and 11 are not yet vaccinated," he said. "So that's an opportunity for us to expand vaccination in our community and further reduce hospitalizations."
A Covid-19 vaccine for children younger than 5 is also expected, but likely won't be available until mid-2022.
In the meantime, measures including masking up, testing and contact tracing can help keep young children safe. When asked whether parents should feel safe sending young children back to school, Kociolek said schools are generally safe and "oftentimes safer than the community."
"We saw last year in Chicago that cases spiked between Thanksgiving and the New Year and as soon as school started, cases in children declined," he said. "And when our research team went into schools in Chicago and looked we saw very little to no evidence (of transmission)."
The rise in pediatric hospitalizations now comes as the Omicron variant -- the most contagious coronavirus strain yet -- is quickly spreading, coupled with community activity that "shot up very, very quickly," Kociolek said.
With reports that Omicron may present milder symptoms, the doctor added it's important for parents to remember that mild cases can be contagious, too -- and that in order to keep schools open, parents should keep sick children home from school and other activities. He suggested they can also get their children tested before returning to school to ensure they're not bringing the virus to the classroom.
"I'm confident that school is very, very safe and as a parent I plan on sending my children back to school without concerns of transmission," he said.