Omicron Drives Covid-19 Child Hospitalizations to New Highs

In England, 576 children ages 5 and under were admitted to hospitals with Covid-19 in the week to Jan. 9, well above the previous peak of around 160 in August. Separate data, from a study that tracks admissions in detail from around half the hospitals in the U.K., show that the rise is being driven by under-ones. Admissions for those ages 6 to 17 are also at a high. By contrast, Covid-19 hospitalizations among adults are still significantly below the peaks of earlier waves, thanks in large part to vaccination.

Those numbers appear alarming, but doctors say there are no clear signs, so far, that Omicron is afflicting children worse than earlier variants. What is likely contributing to the pattern is that the unprecedented number of infections across the country means that more children have it when entering hospitals, often for respiratory diseases they commonly get in winter. In other words, the proportion of children going into hospitals with Covid-19 rather than because of the disease is likely significantly higher than in adults.

The rate of Covid-19 hospital admission among children ages 5 and under, at around 15 per 100,000 for the week to Jan. 9, is still lower than in adults, where rates range from 17 per 100,000 among those ages 18 to 64, to 179 per 100,000 in those 85 and older.

But the figures don’t say much about how much Covid-19 is responsible for sending children to the hospital. They encompass those there primarily for another reason—such as a broken leg—who have tested positive for the virus before or after they were admitted. They also include those in the hospital for other infections or illnesses where Covid-19 might have played a part.

Covid-19 vaccines aren’t routinely offered to children under the age of 12 in the U.K., but it isn’t known, doctors say, whether this plays a significant role.

“It would be rather surprising if we didn’t see large numbers of hospital admissions with the infection,” because of the high level of cases in the community, said Adam Finn, professor of pediatrics at the University of Bristol. “The tricky bit is trying to figure out how much the infection is actually contributing to the reason for the child being in hospital,” he added. “It’s not cut and dried.”

Doctors say that more children are being treated primarily for Covid-19, but no more than would be expected given the sheer number of infections Omicron is causing. Separate data show that overall case numbers in those ages 4 and below in England have quadrupled since the beginning of November.

And Omicron doesn’t appear to be leading to a surge in the most severe cases among children. Data from the U.K. Health Security Agency show that intensive-care-unit admissions for those ages 4 and below didn’t rise significantly during December, despite a quadrupling in hospital admissions among that group.

“These are not particularly sick infants,” said Calum Semple, professor in child health and outbreak medicine at the University of Liverpool, one of the researchers on the hospital admissions study. They are being admitted for shorter periods in this wave and requiring less oxygen than in previous surges of the virus, he said. The proportion taken to ICU has slowed over time and the numbers on mechanical ventilation are incredibly low and continue to fall, he added.

Edward Dallas, a consultant pediatrician in the emergency room in a London hospital, said he is probably seeing more children with Covid-19 in this wave than at any time in the pandemic, but didn’t think that was because Omicron is affecting children more severely, just affecting more children.

He added that the most common symptoms of Omicron infection in children appeared to be runny nose and cough but that it didn’t typically lead to lung infection.

“It’s just a pure numbers game,” said Chethan Sathya, a pediatric surgeon at Northwell Health’s Cohen Children’s Medical Center in New York, where cases are also surging. “If you look at the positivity rates, they’re through the roof.”

Another complicating factor is that it is common during the winter for young children to go to hospitals for respiratory illnesses and test positive for several different viruses, making it impossible to determine which is the root cause.

“Over time we see more Covid co-infection,” said Ronny Cheung, a consultant pediatrician at a hospital in London. “Anyone who tries to say [the illness] is because of Covid or another respiratory infection is making it up as they go along.”

Hospital admissions among babies are especially likely to move in lockstep with the background infection rate because the threshold for admission is low in very young children. For instance, children six months and under who got to the hospital with a fever are typically admitted for routine tests and monitoring, as a precaution. The hospital admissions study found that babies made up a larger proportion of hospital admissions among children, around 42%, in the past four weeks, up from around 30% during the Delta wave.

“We know Covid gives you a fever and if you are febrile and an infant you are going to go through an investigation cycle,” said Damian Roland, honorary professor of pediatric emergency medicine at the University of Leicester. “It doesn’t necessarily mean Covid is any worse or particularly harmful.”

“Just like any other virus, when you’ve got more of it around you’ll see more children coming in, and more will tip the threshold for needing admission,” said Jane Bayreuther, chair of the U.K.’s Association of Paediatric Emergency Medicine. There has been no increase in the overall severity, she added.

Still, it’s too early to tell the full extent of the impact of the new variant in children, according to Chinedu Nwokoro, a consultant respiratory and general pediatrician in a London hospital.

An “Omicron-sized blip” in any condition linked to infection with Covid-19 in children, including long Covid and multisystem inflammatory syndrome, or MIS-C—a rare inflammatory condition affecting some children around six weeks after infection with the virus—is “in itself is going to be a problem,” Dr. Nwokoro said.

“Given [MIS-C cases] tend to present several weeks after the initial infection, we are bracing ourselves for a bigger rise over coming weeks,” said Dr. Cheung. “The question is: Will Omicron do something different?”

Analysis of the health records of more than 14,000 children under 5 years old in the U.S. comparing those infected with Omicron with those who had Delta found the newer variant was significantly less likely to lead to severe outcomes. The study, from researchers at the Center for Artificial Intelligence in Drug Discovery in Cleveland, hasn’t been peer reviewed.

At Advocate Children’s Hospital, which is run out of two sites near Chicago, Covid-19-related hospitalizations increased more than threefold in the 30 days to Jan. 6, according to chief medical officer Frank Belmonte. Around a quarter of patients on average each day are ending up in pediatric intensive-care units, he added, up from around 10% on average in previous waves.

Some of the children in Advocate’s intensive-care unit didn’t have prior risk factors for Covid-19, according to Nekaiya Jacobs, a pediatric critical-care physician at the hospital. “There continues to be this misconception that Covid is always mild in children or teens or that children just don’t get sick,” she said.

Write to Denise Roland at Denise.Roland@wsj.com and Joanna Sugden at joanna.sugden@wsj.com