COVID-19 mRNA vaccine effectiveness against hospitalizations among U.S. children and adolescents during Omicron variant predominance

Presenter: Laura D. Zambrano, PhD, Senior Epidemiologist at the U.S. Centers for Disease Control and Prevention, Atlanta, GA, United States

In a case-control study of COVID-19 mRNA vaccination effectiveness for preventing pediatric hospitalizations, during Omicron variant predominance, protection waned over time but still reduced the likelihood of COVID-19 hospitalization by more than 60%, according to Laura D. Zambrano, PhD, Senior Epidemiologist at the Centers for Disease Control and Prevention, Atlanta, GA, United States. Nearly three-fourths of children who required life support or who died were unvaccinated, she said in an ID Week 2023 oral presentation.

Describing COVID-19 burden and vaccination in children, Zambrano noted that while severe COVID-19 outcomes in children age 5 to 18 years are rare, about 200 per 100,000 children have been hospitalized for COVID-19, with intensive care unit (ICU) admission rates of 20% to 30%. Invasive mechanical ventilation is needed in up to 10%, and over 9,000 cases of multisystem inflammatory syndrome in children have been reported to the CDC.1

At the same time that emerging SARS-CoV-2 Omicron variants have increased vaccine-induced immune evasion, COVID-19 vaccine effectiveness has waned. The aim of the current study was to examine severe outcomes and critical illness among children aged 5 to 18 years, providing updated estimates of vaccine effectiveness against pediatric hospitalizations that reflect expanded patient population during the period Omicron predominance, vaccine effectiveness relative to time since the last vaccine dose, and bivalent mRNA vaccines. Also, the goal was to examine the association with protection against COVID-19 ICU admissions. Zambrano noted that COVID-19 mRNA vaccines, whose efficacy has repeatedly been reported,2 have been available for all persons over the age of 5 years since November 2021.

In this study report, Zambrano and colleagues focused on the older age group of children: from 5 to 18 years. In their analysis, they sought to enroll all children who were hospitalized during the period of Omicron predominance from December 19, 2021 through August 26, 2023. They used a case-control design, with case patients defined as children hospitalized with COVID-19 ages 5 to 18 years, who were matched to controls by site, age group, and approximate date of hospital admission. Controls were defined as having “COVID-like illness” while testing negative for SARS-CoV-2 by reverse transcription polymerase chain reaction and for influenza.

The analysis matched 1,539 SARS-CoV-2-positive cases, of whom 800 (52.0%) were ages 5 to 11 years, with 1,680 SARS-CoV-2 negative controls, of whom 948 (56.4%) were ages 5 to 11 years. Compared with controls, case patients had a significantly higher frequency of underlying medical conditions, specifically cardiac, respiratory, and neurologic conditions, and immunocompromised and unvaccinated status. Only 29 case patients and 35 controls had received a bivalent booster dose.

For children ages 5 to 18, vaccine effectiveness against COVID-19-associated hospitalizations in the first 60 days was 64.6%, waning thereafter but still offering some protection beyond 8 months. Bivalent vaccine coverage was low, precluding precise estimates.

Among children ages 12 to 18, vaccine effectiveness was 57.1% within the first 60 days, again waning after 60 days, but with significant protection persisting throughout the first 7 months. The sample of children receiving bivalent doses was too small for estimates.

Vaccine effectiveness against COVID-19-associated ICU admissions overall was 81.4% within the first 60 days, but waned to 35.3% after 120 days. Significant protection against critical illness, however, did persist beyond 8 months. Again, relatively few children received bivalent vaccine.

Bivalent vaccine coverage remained below 10% across all groups. Analysis of cases and controls by underlying condition status, Zambrano reported, revealed that no child who was otherwise healthy and received a bivalent dose was hospitalized for COVID-19. Also, the 29 case patients who received a bivalent dose all had multiple underlying conditions.

Zambrano concluded, “Children who were hospitalized for COVID-19 were significantly less likely to have been vaccinated.” She added that vaccination confers strong protection against ICU admission, and that although some waning may occur after 60 days, vaccine effectiveness remains significant. She noted also that all of the case patients who received bivalent vaccine had multiple underlying medical conditions.

Disclosures. Dr. Zambrano had no disclosures to report.

References

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