During the peak of the Omicron wave, weekly hospitalizations for infants and toddlers due to COVID-19 were approximately five times what they were during the peak of the Delta variant, new research from the CDC showed.

In the first week of January, COVID-associated hospitalizations in children ages 0-4 years reached 14.5 per 100,000 children, reported Kristin Marks, PhD, and the COVID-NET Surveillance Team in the Morbidity and Mortality Weekly Report.

Of those hospitalized during Omicron’s predominance, 63% had no underlying medical conditions. Infants younger than 6 months of age were hospitalized at six times the rate they were during the Delta variant’s predominance (rate ratio 6.1, 95% CI 3.9-10.0). During the two waves, hospitalizations in kids under 6 months of age accounted for 43% to 44% of all hospitalizations among children ages 0-4 years, according to the report.

“Although infants aged <6 months are not currently eligible for vaccination, evidence suggests that this age group can receive protection through passive transplacental transfer of maternal antibodies acquired through vaccination,” Marks and colleagues wrote.

“CDC recommends that women who are pregnant, breastfeeding, trying to become pregnant, or might become pregnant get vaccinated and stay up to date with COVID-19 vaccination,” they added. Marks’ group also recommended that family members and caregivers get vaccinated.

This study supports previous reports showing that hospitalizations for young children surged during Omicron. Currently, only children ages 5 and older are eligible for a COVID vaccine, and only those 12 and older are eligible for a booster shot.

Monthly intensive care unit (ICU) admission rates were around 3.5 times higher during the Omicron peak compared with the Delta peak, though a higher proportion of infants hospitalized during Delta predominance required ICU admission (27% vs 21%, P=0.02), Marks and team noted. Hospital length of stay during Omicron predominance was also shorter than during Delta (2 vs 1.5 days, P=0.002).

Hospitalization rates for children ages 0-4 years began to fall in mid-February, they said.

Notably, among over 1,500 children (about 62% of the study cohort) who were tested for additional pathogens, one-fifth were hospitalized with respiratory syncytial virus (RSV) co-detections during Delta predominance compared with only 7% during Omicron predominance (P<0.001).

This pattern supports trends in RSV circulation seen in other studies, the researchers noted, as it increased during the summer and fall of 2021 and decreased in the winter.

“These limited data suggest that the surge in hospitalizations during Omicron predominance was not driven by co-infections,” Marks and colleagues wrote.

Young infants were more likely to have been hospitalized with RSV co-detections compared with older children, with 13% of those younger than 6 months hospitalized compared with 4% of children ages 6 to 23 months and 2% of children ages 2 to 4 years.

However, length of stay, ICU admission, and use of respiratory support did not differ significantly by age, Marks and colleagues reported.

“Future studies are needed to understand the possible long-term consequences of COVID-19 infection among infants,” they wrote.

This study was part of COVID-NET, which conducts surveillance studies in hospitals across 14 states. It included data on over 2,500 children ages 0-4 years who were hospitalized from March 2020 to mid-February 2022. Of these children, 85% had COVID-19 as the primary reason for admission.

The study period was divided into three periods depending on which variant accounted for over half of sequenced isolates: March 2020 to June 26, 2021 was considered the pre-Delta predominance period; June 27 to Dec. 18, 2021 was the Delta predominance period; and Dec. 19, 2021 to Jan. 31, 2022 was the Omicron predominance period.

Marks and colleagues noted that their study could not account for differences in testing practices or public health policies that could have influenced COVID spread.

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