(CNN) — More children are getting hospitalized with Covid-19 than ever before as the Omicron variant’s dominance intensifies.

An average of 672 children were admitted to hospitals every day with Covid-19 during the week ending Sunday, the highest such number of the pandemic, according to data from the US Centers for Disease Control and Prevention.

It follows a record-high number of new Covid-19 cases among children, according to the American Academy of Pediatrics (AAP).

The US had more than 325,000 new cases among children during the week ending December 30, according to data published this week by the AAP, marking a 64% increase in new childhood cases compared to the previous week, the AAP said.

And across all age groups, Covid-19 hospitalizations reached a new milestone.

On Tuesday, 112,941 Americans were hospitalized with Covid-19, according to data from the US Department of Health and Human Services.

The new figure far exceeds peak hospitalizations during the Delta variant surge — nearly 104,000 in early September. It’s also creeping toward the pandemic-high number of Covid-19 patients hospitalized in a single day — 142,246, on January 14 of last year.

“Unfortunately, this is the consequence of a highly transmissible variant, the Omicron variant,” US Surgeon General Dr. Vivek Murthy told CNN on Tuesday.

In just four weeks, Omicron jumped from an estimated 8% of new Covid-19 infections to an estimated 95% of new infections, according to the CDC.

Now, more hospital intensive care units are nearing capacity.

Nationwide, 1 in 5 hospitals with an ICU said its beds in that unit were at least 95% full last week, according to DHHS data. And more than a quarter of ICU beds nationwide were occupied by Covid-19 patients.

The surgeon general reiterated what many doctors have reported this winter: The vast majority of hospitalized Covid-19 patients are not vaccinated and boosted.

“Remember, those vaccines work. Those boosters are more important than ever before,” Murthy said.

And millions more children heading back to school may soon be able to get a booster shot.

FDA authorizes Pfizer booster doses for kids ages 12 to 15

The rapid spread of the Omicron variant helped spur the US Food and Drug Administration to authorize booster doses of Pfizer’s Covid-19 vaccine for children 12 to 15, FDA Acting Commissioner Dr. Janet Woodcock said Monday.

For everyone ages 12 and up, the FDA also shortened the time needed between the second dose of the Pfizer vaccine and the booster dose — from six months to five months.

CDC Director Dr. Rochelle Walensky supported reducing the time needed before a booster dose. The agency’s vaccine advisory board is due to meet Wednesday to discuss expanding booster eligibility to 12- to 15-year-olds.

The FDA has also authorized booster doses for some children ages 5 to 11 who are immunocompromised, including those who have received an organ transplant.

‘Staggering numbers’ of Omicron cases at pediatric hospital

At the nation’s largest pediatric hospital, Covid-19 hospitalizations have quadrupled in just the past two weeks — fueled by the Omicron variant, the most contagious strain of novel coronavirus to hit the US.

“We have staggering numbers here from this Omicron surge already,” said Dr. Jim Versalovic, pathologist-in-chief at Texas Children’s Hospital in Houston.

“We shattered prior records that were established during the Delta surge in August.”

Sequencing showed 90% of the hospital’s recent Covid-19 patients had been infected with the Omicron variant, Versalovic said.

Like the surgeon general, Versalovic said vaccinations are critical to minimizing Covid-19 hospitalizations.

Yet more than 80% of school-age children in the Houston area are unvaccinated, Versalovic said.

And more than a third of the hospital’s recent Covid-19 patients have been under age 5. “Unfortunately, those children still do not have access to a vaccine,” Versalovic said.

In New York, “We are seeing more Covid now than we have seen in previous waves,” pediatrician Dr. Edith Bracho-Sanchez said.

“And it’s worrisome that the worst of the winter here has not passed. And we are bracing for what is still to come.”

Doctors: Don’t underestimate the impact on children

Pediatricians have acknowledged some patients with Covid-19 may have actually sought treatment for another condition and happened to test positive for coronavirus.

But “it’s clear that the majority of cases either have Covid-19 as a primary factor or as a significant contributing factor to their hospitalization,” said Versalovic, the pathologist-in-chief at Texas Children’s.

And the recent record-setting number of pediatric Covid-19 hospitalizations — along with the severe illness among some children — means the current surge shouldn’t be ignored.

“We would be foolish to keep minimizing Covid-19 in children at this point in the pandemic,” Bracho-Sanchez said.

Early studies suggested Omicron causes less severe disease than the Delta variant. But Omicron is much more contagious.

And early research suggested Omicron may cause more upper-airway problems, unlike previous strains causing lower-airway problems.

Upper airway complications can be more dangerous for young children than for adults, Bracho-Sanchez said.

“We cannot treat the airways of children like they are the airways of adults,” she said.

“And for us pediatricians, we know that respiratory viruses can lead to … croup and bronchiolitis, that inflammation of the upper airways that does get in children in trouble.”

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