2081. COVID-19 mRNA Vaccine Effectiveness against Hospitalizations among U.S. Children and Adolescents During Omicron Variant Predominance
Authors: Zambrano Laura D , Newhams Margaret M , Wu Michael J , Simeone Regina , Orzel Amber , Halasa Natasha B , Fleming-Dutra Katherine E , Campbell Angela P , Randolph Adrienne G 
Published: November 2023

Abstract

Background
SARS-CoV-2 Omicron variants have increased vaccine-induced immune evasion and their emergence coincided with waning COVID-19 vaccine effectiveness (VE). The duration of immunity from the primary series and VE of booster doses against pediatric COVID-19 (Omicron)-associated hospitalizations has not been characterized in the United States.

Methods
Using a case-control design, we examined VE against laboratory-confirmed COVID-19-associated hospitalizations, enrolling case-patients hospitalized for COVID-19 and SARS-CoV-2 test-negative controls with COVID-like illness from 31 hospitals in 23 states. VE was estimated through multivariable logistic regression by comparing the odds of antecedent primary series or booster COVID-19 mRNA vaccination within and beyond 60 days prior to hospitalization. Results were analyzed by age group (5–11 and 12–18 years) among patients admitted December 19, 2021–March 30, 2023.

Results
We enrolled 1,242 case-patients (972 [78%] of whom were unvaccinated, 164 [13%] of whom received life support, and 11 of whom died) and 1,309 controls. Among children aged 5-18 years, VE of 2 mRNA doses (complete primary series) against pediatric COVID-19 hospitalization was 64% (95% confidence interval [CI]: 44–76%) at 14-60 days after dose 2 (median time since dose 2, 38 days); VE waned to 38% (95% CI: 23–50%) at ≥60 days (median time since vaccination, 213 days). Within 60 days of a monovalent booster dose, VE was 52% (95% CI: -3–77%); among children aged 5-11 years, VE of a bivalent booster dose was 79% (95% CI: 25-94%). Among case-patients who required life support or died, 122/164 (74%) were unvaccinated and only 3 (2%) had received a bivalent booster dose.Figure 1.Vaccine effectiveness against COVID-19-related hospitalizations, by age group, vaccine dose, and time since last dose.
VE estimates were only plotted if confidence interval width was &lt;200. Adjusted models included ≥1 underlying medical condition (yes/no), age in years, census region, biweekly date of hospital admission, and social vulnerability index (SVI) score. Sex and race/ethnicity were tested as confounders in the full model but were dropped for absence of evidence of confounding.Table 1.Critical outcomes among enrolled COVID-19 case-patients ages 5-18 years, by vaccine dose and time since last vaccine dose.
Abbreviations: ICU, intensive care unit; ECMO, extracorporeal membrane oxygenation

Conclusion
COVID-19 mRNA vaccination reduced the likelihood of pediatric COVID-19 hospitalization by &gt;60%; VE waned but remained protective, even at a median of 213 days after dose 2. Although not reaching statistical significance due to limited power, monovalent boosters appeared to temporarily restore protection, and bivalent booster doses among 5–11-year-olds were nearly 80% protective against hospitalization. Nearly three quarters of children requiring life support or who died were unvaccinated.

Disclosures
Regina Simeone, PhD, Pfizer: Stocks/Bonds Natasha B. Halasa, MD, MPH, Merck: Grant/Research Support|Quidell: Grant/Research Support|Quidell: donation of kits|Sanofi: Grant/Research Support|Sanofi: vaccine support