The number of young children hospitalized with the coronavirus rose rapidly last week to the highest level since the start of the pandemic, according to data released Friday by the Centers for Disease Control and Prevention.
The increase was seen in children 4 years and younger, who were not eligible for vaccination, and the data included children admitted to hospital for reasons other than Covid.
The increase can be partly explained by the increase in Omicron cases, which affect all populations, and the spread of other respiratory infections.
But the data doesn’t show a similarly sharp rise in coronavirus infections among hospitalized children of other ages, and federal health officials considered the possibility that Omicron may not be as mild in young children as it is in older children.
Children infected with the variant are still much less likely to become seriously ill compared to adults, and even young children seem to need ventilators less often than those admitted during previous peaks, doctors said.
“We have not yet seen a signal of increased severity in this age group,” said Dr. Rochelle Walensky, the director of the CDC, told reporters during a news conference Friday.
More than four in every 100,000 children aged 4 and under admitted to hospitals were infected with the coronavirus on January 1 – double the number reported a month ago and about three times the number this time last year.
In contrast, the number of 5- to 11-year-olds hospitalized with Covid was 0.6, about the same figure reported in recent months.
dr. Walensky noted that only 16 percent of children ages 5 to 11 had been fully vaccinated, and she urged anyone eligible for vaccines and boosters to get them as soon as possible.
“Unfortunately, we are seeing an increase in hospital admissions for children aged 0 to 4, who are currently not yet eligible for Covid-19 vaccination,” she said. “It’s critical that we surround them with people who have been vaccinated to protect them.”
The increase is noticeable at a number of regional medical centers. The hospitalizations of young children are “blowing away our previous late summer, early fall Delta wave, which had been the highest before,” said Dr. Danielle Zerr, a pediatric infectious disease expert at Seattle Children’s Hospital.
Experts are generally cautious about interpreting an increase in pediatric hospitalizations as a sign that a variant is particularly severe in children compared to adults. There were similar fears about the Delta and Beta variants, but the increase in the number of children’s hospitals turned out to be more a result of the contagiousness of the variants.
This time again, at least part of the increase in the number of cases is a reflection of the increase in Omicron in all age groups. The nation now records an average of about 600,000 cases per day, about one in five in children.
“The more children become infected, the more children will be sick enough to be hospitalized,” said Dr. Yvonne Maldonado, chair of the infectious diseases committee at the American Academy of Pediatrics and a physician at Stanford University.
At Seattle Children’s Hospital, for example, about 21 percent of children test positive for the coronavirus, compared with the average of about 1 percent and a peak during the Delta wave of about 3 percent.
“That’s just a game changer,” said Dr. Zerr about the more recent figures.
Doctors may admit a young child more quickly than an adult with similar symptoms, which may explain some of the rising rates in young children. But some experts said the rise this time may be too steep to be explained by the usual factors alone.
An alternative hypothesis for the rise may be that young children are particularly vulnerable to upper respiratory tract infections — exactly where Omicron is reportedly more concentrated compared to other variants.
“They’re smaller, their airways are smaller,” said Dr. Kristin Oliver, a pediatrician at Mount Sinai Hospital in New York, on young children.
“It seems reasonable in a disease that if it appears to affect the upper respiratory tract more, they are affected more,” she added. “They’re more at risk for that — for longer, long-term cases, as well as the hospitalization that can accompany a more serious case.”
That may explain why more hospitalized children aged 4 and under have tested positive for the coronavirus than children aged 5 and older. It’s also why young children are more vulnerable to other pathogens, such as respiratory syncytial virus, and to the seal-like cough associated with croup.
For parents of young children, the numbers add another concern as they wait for vaccines to become available.
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Alicia Henriquez, a public school teacher in Chicago, has three children, two of whom are under 5. Her younger children — Maxi, 4, and Sofia, 2 — are both infected with the coronavirus, but Maxi has no symptoms at all, and Sofia cough alone.
Still, Ms. Henriquez said she kept a close eye on their symptoms. “You don’t know if your child will end up in the hospital or not, so I think you still need to be careful,” she said.
The CDC’s new data was collected by Covid-Net, the agency’s hospital admissions network, which spans 14 locations and covers about 10 percent of the U.S. population. The rates have likely been underestimated, according to the agency, due to the lack of availability of tests.
Many children who become seriously ill have other conditions or have weak immune systems. “Those kids are definitely at high risk right now,” said Dr. maldonado. “We see them now more than before.”
dr. Julie Binder, a gastroenterologist in Philadelphia, has two daughters under 5. Her oldest daughter, Annie, 4, has an undiagnosed medical condition that results in “some very bizarre reactions” to viruses, said Dr. Binder. After Annie ended up in the hospital due to a viral infection two years ago, she had complications for months.
dr. Binder and her husband are adamant about maintaining as normal a life as possible for Annie, even during the pandemic. But they’ve kept her home from daycare for the past few weeks to protect her from the spike in infections after the holidays.
“When I heard this information, I’m certainly glad I did,” said Dr. Binder on the data released Friday. “I would have felt much more comfortable now with this wave if she had been vaccinated.”
A coronavirus vaccine is not yet available in the United States for children under the age of 5, and is unlikely to be for a few more months. But many older children have not yet been vaccinated.
Less than 25 percent of children ages 5 to 11 and just over 60 percent of adolescents ages 12 to 17 have received at least one dose of a coronavirus vaccine.
“If you’re really concerned about your child getting sick, you should vaccinate your child,” said Dr. maldonado. “It’s the easiest thing we can do right now to keep our kids healthy.”
As of October 31, about one in three children hospitalized with Covid was obese. Still, about half had no other known medical conditions, according to data collected by the CDC