(CNN) — With tens of millions of unvaccinated Americans at higher risk for severe disease from Covid-19 infections, doctors and health care facilities nationwide are reporting a rising number of young people hospitalized, some of whom are too young to receive vaccine doses.

The nation’s largest pediatric hospital, Texas Children’s Hospital in Houston, is reporting a more than four-fold increase in child hospitalizations from Covid-19 over the last two weeks, spurred by the spread of the Omicron and Delta variants over the holiday season.

“We have staggering numbers here from this Omicron surge already,” Dr. Jim Versalovic, pathologist-in-chief at Texas Children’s, said Monday. “We shattered prior records that were established during the Delta surge in August.”

More than 700 children were in the hospital with Covid-19 during one 24-hour period last week, he said, and 90% of cases were shown through sequencing to have been caused by the Omicron variant.

“We are seeing more Covid now than we have seen in previous waves,” said Dr. Edith Bracho-Sanchez, a primary care pediatrician and assistant professor of pediatrics at Columbia University Irving Medical Center in New York, “and it’s worrisome that the worst of the winter here has not passed, and we are bracing for what is still to come.”

Noting that some children who have coronavirus may be seeking medical care for other conditions yet testing positive, Bracho-Sanchez told CNN’s Anderson Cooper Monday it is evident from what she has seen in New York City that more children there have Covid-19 than ever before.

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

Early research suggests Omicron may cause more upper airway problems, unlike previous strains that caused lower airway problems. However, upper airway conditions can be more dangerous for children than adults.

“We cannot treat the airways of children like they are the airways of adults,” she said. “It’s just not the way it works. 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.”

Versalovic said Monday of the children at their facility needing care, “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.”

Data published from the US Centers for Disease Control and Prevention (CDC) and the Department of Health and Human Services last week showed that pediatric hospital admissions had reached a record high, eclipsing marks from the 2020 holiday surge as well as the Delta surge over the summer and fall.

Cumulative hospitalization rates through November are about eight times higher for unvaccinated adults and about 10 times higher for unvaccinated children ages 12 to 17, according to CDC data.

Children are the least vaccinated age group in the US, with around 53% of ages 12-17 fully vaccinated and those ages 5-11 far less, according to CDC data. Americans at age 18-24 are nearly 59% fully vaccinated and those ages 25-39 are at 63%.

Overall, 62% of the US population is fully vaccinated and more than 33% of those have received a booster, CDC data shows.

Booster eligibility expands to more teens

Health officials and experts continue to beseech Americans that the most effective way to avoid hospitalization is through vaccination. And not only has the effectiveness of vaccination been demonstrated in keeping more people safe, but booster doses for those eligible can improve protection against Omicron.

Access to boosters — widely available to those over the age of 16 — was increased Monday after the US Food and Drug Administration (FDA) expanded the emergency use authorization for Pfizer/BioNTech’s Covid-19 vaccine boosters to children ages 12 to 15.

The agency also shortened the time needed before receiving a booster shot from at least six months after completion of the initial series to at least five months, for everyone 12 and older.

About 5 million of the ages-12-to-15 population have been fully vaccinated for more than five months and are now eligible to receive a booster shot, according to the CDC.

With children ages 5 and up able since October to be vaccinated, CNN medical analyst and emergency physician Dr. Leana Wen asked of parents and guardians Monday, “What are you waiting for?”

“This is the time that’s the most dangerous for our children and the entire pandemic because of how widespread Covid is. There is just virus everywhere. Please get your children vaccinated,” she said, adding that school-age children who are inoculated will contribute to protecting younger siblings through lowered risks of infection.

“That is the whole idea of herd immunity, to protect those who need our help the most,” she said.

Vaccine makers are working to develop doses for those under the age of 5, yet the earliest timeline for rollout is in the spring or summer.

‘We’re not in a good place’

The Omicron variant has led to a massive surge in Covid-19 cases since its arrival stateside was announced last month, compounding the Delta surge already in progress and pushing some school districts to return to online learning or in-person mask wearing until infections subside.

Evidence points to Omicron being less likely to cause severe disease than Delta, however its transmissibility means many more will be infected, overwhelming health care systems. And areas of concern are sprouting up nationwide.

“We’re not in a good place, I’m going to be really honest with you,” New York Gov. Kathy Hochul said Monday. “This is the winter surge we predicted.”

Regarding the high rate of infections overall, “the severity of the illness is far less than we’ve seen before,” she said, yet the number of those hospitalized is going up.

Mobilized with support from the National Guard, Ohio is opening new Covid-19 testing locations in nine cities this week, Gov. Mike DeWine announced. The state now has more coronavirus hospitalizations than at any other point in the pandemic, according to the Ohio Hospital Association.

And Nevada is “seeing an alarming number of Covid-19 cases and hospitalizations reported after the end of the year holidays,” Gov. Steve Sisolak said in a statement. “My team is continuing to analyze the numbers and we are working with health districts and other partners to provide resources to combat the surge we are facing.”

(Copyright (c) 2024 CNN. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)

Join our Newsletter for the latest news right to your inbox