Only 4.5% of a cohort of pediatric COVID-19 patients admitted to US hospitals during the period of Omicron predominance had completed their primary COVID-19 vaccine series, and 7.0% had started but didn't finish the series, The Pediatric Infectious Disease Journal reports.
The study team, led by Centers for Disease Control and Prevention (CDC) researchers, enrolled 597 vaccine-eligible COVID-19 inpatients aged 8 months to 4 years at 28 hospitals participating in the Overcoming COVID-19 network from September 2022 to May 2023. A total of 62.1% of patients were aged 8 months to 1 year, and 37.9% were aged 2 to 4 years.
A complete vaccination series was defined as at least two Moderna or three Pfizer/BioNTech mRNA COVID-19 doses received at least 14 days before hospitalization.
Most very ill patients were unvaccinated or partially vaccinated
The vast majority of patients (88.4%) were unvaccinated. Most children (74.1%) who completed the primary COVID-19 vaccine series were White. Completion of the vaccine series was low in all regions but highest in the Northeast (12.2%) and lowest in the South (1.5%).
In total, 4.5% of the children had completed their primary COVID-19 vaccination series, and 7.0% started but did not complete their primary series. Of the 528 unvaccinated patients, 48.0% were previously healthy, 3 needed extracorporeal membrane oxygenation (ECMO), and 1 died.
Most critically ill children were unvaccinated or hadn't completed their primary series, including 94.3% of children admitted to an intensive care unit (ICU), 88.2% who received invasive mechanical ventilation (IMV), and 92.0% with life-threatening infections. This included all three patients who required ECMO and the 29 who required vasopressors to maintain their blood pressure.
All six critically ill patients who completed their vaccine series and were hospitalized had one or more chronic respiratory or neurologic conditions, including four who had both.
Among children younger than 2 years, 44.7% had at least one underlying illness, compared with 69.9% of those aged 2 to 4. The most common underlying conditions were respiratory or neurologic/neuromuscular. A small proportion (1.2%) of children also had influenza, and 11.4% also had respiratory syncytial virus (RSV).
Overdue doses more common in Pfizer recipients
Of the 597 children, 29.1% were admitted to an ICU, and 12.6% had a life-threatening illness, including 8.5% needing IMV. Children with chronic respiratory and neurologic/neuromuscular illnesses were most likely to need high levels of respiratory support.
Of the 42 patients but didn't complete their primary vaccination series before hospital admission, 33 were overdue for a dose, and 9 were hospitalized between doses but weren't overdue for the next dose. Overdue doses were more common among those who started the Pfizer vaccine series (81.8%) than among Moderna initiators (18.2%).
The longer timeframe required to complete the 3-dose Pfizer-BioNTech primary series may also allow for more opportunities for infection during inter-dose intervals.
The authors said that low vaccine uptake in this age-group may be due to logistical challenges, including problems with vaccine distribution, reliance on pediatricians and hospitals rather than pharmacies to give doses to very young or medically complex patients, and the relative complexity of the Pfizer vaccine series (three doses given at different intervals).
"The longer timeframe required to complete the 3-dose Pfizer-BioNTech primary series may also allow for more opportunities for infection during inter-dose intervals," they wrote.
The findings underscore the importance of improving COVID-19 vaccine uptake and awareness of disease severity in young children, the researchers said. "Despite an observed decrease in the proportion of hospitalized children <5 years of age requiring ICU admission during the period of Omicron predominance, similar proportions are still requiring IMV," they wrote.
