“The bigger picture here is that covid can be a severe disease, even in young children and even in otherwise healthy children,” said William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, who had no involvement in the study. “Although the risk of severe disease is higher in older adults than in children, children are not spared covid-19, and even otherwise healthy children without underlying health conditions can be hospitalized.”
Omicron is a more highly transmissible variant that caused more people in every age group to get sick, including more small children, Moss noted. But it did not cause more severe infections than previous variants — the proportion of hospitalized children who ended up in the intensive care unit was smaller during the omicron wave than it was during the delta wave that began last summer and continued through fall and winter.
About 63 percent of those hospitalized children had no underlying medical conditions and 44 percent were infants under 6 months, the study found.
Besides omicron’s transmissibility, experts theorize that another reason for the jump in hospitalizations is the more vulnerable upper airways of infants and very young children.
“If you’re dealing with a variant that has a propensity for upper airway infections, naturally you’re going to see more symptomatic disease in younger children,” said Mark Kline, physician in chief and chief medical officer at Children’s Hospital New Orleans, who did not participate in the CDC study. “They start out with an airway that is narrower and much more easily blocked by inflammation.”
Kline said that during the omicron wave, Children’s Hospital admitted more infants and children with croup-like symptoms — including barking coughs and raspy breathing — and far fewer children with covid pneumonia. While upper airway infections are often easier to treat and relatively common, he said, the hospital still had many patients in the ICU and some children died during the winter surge.
“People were saying omicron seemed to be milder than delta, and I think that’s because it was less likely to involve the lung, but it’s not an all-or-none thing,” Kline added. “We did see some kids with omicron who were seriously ill, and we even had some deaths.”
Another factor in the high hospitalizations may be that infants and other young children belong to the only demographic in the United States who are not yet eligible for vaccines. To protect them, the CDC recommends vaccinations of the adults and older children around them. Pregnant people are also encouraged to get vaccinated, both to protect themselves from a higher risk of severe infection and to pass that protection onto their babies.
“We need strategies to protect children, and those strategies include … protecting children by protecting the people around them and vaccinating their parents and caregivers,” Moss said.
Efforts to prevent illness in the youngest children are also important because some children — even those who do not suffer severe covid-19 — may later develop a rare but serious condition called MIS-C, or multisystem inflammatory syndrome in children. MIS-C can lead to hospitalization and death in severe cases.
Despite the increase in pediatric hospitalizations during the omicron surge, some metrics related to hospital stays improved, in part because the variant did not cause as much severe illness as earlier versions.
The length of hospital stays for infants and other young children was slightly shorter during omicron, lasting an average of one and a half days compared to two days during the peak of the delta wave. And 21 percent of hospitalized children under 5 required intensive care during omicron, compared with 27 percent at the height of the delta surge.
Hospitalizations among young children peaked during the week of Jan. 8, when there were 14.5 per 100,000 infants and other children under 5. That was about five times higher than the hospitalization rate of 2.9 per 100,000 children in that age group when the delta variant peaked in early September, the CDC report said.