Durability of Original Monovalent mRNA Vaccine Effectiveness Against COVID-19 Omicron–Associated Hospitalization in Children and Adolescents — United States, 2021–2023

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Pediatric COVID-19 vaccination is effective in preventing COVID-19-related hospitalization, but duration of protection of the original monovalent vaccine during SARS-CoV-2 Omicron predominance merits evaluation, particularly given low coverage with updated COVID-19 vaccines.During December 19, 2021-October 29, 2023, the Overcoming COVID-19 Network evaluated vaccine effectiveness (VE) of ≥2 original monovalent COVID-19 mRNA vaccine doses against COVID-19-related hospitalization and critical illness among U.S. children and adolescents aged 5-18 years, using a case-control design.Too few children and adolescents received bivalent or updated monovalent vaccines to separately evaluate their effectiveness.Most case-patients (persons with a positive SARS-CoV-2 test result) were unvaccinated, despite the high frequency of reported underlying conditions associated with severe COVID-19.VE of the original monovalent vaccine against COVID-19-related hospitalizations was 52% (95% CI = 33%-66%) when the most recent dose was administered <120 days before hospitalization and 19% (95% CI = 2%-32%) if the interval was 120-364 days.VE of the original monovalent vaccine against COVID-19-related hospitalization was 31% (95% CI = 18%-43%) if the last dose was received any time within the previous year.VE against critical COVID-19-related illness, defined as receipt of noninvasive or invasive mechanical ventilation, vasoactive infusions, extracorporeal membrane oxygenation, and illness resulting in death, was 57% (95% CI = 21%-76%) when the most recent dose was received <120 days before hospitalization, 25% (95% CI = -9% to 49%) if it was received 120-364 days before hospitalization, and 38% (95% CI = 15%-55%) if the last dose was received any time within the previous year.VE was similar after excluding children and adolescents with * These senior authors contributed equally to this report.documented immunocompromising conditions.Because of the low frequency of children who received updated COVID-19 vaccines and waning effectiveness of original monovalent doses, these data support CDC recommendations that all children and adolescents receive updated COVID-19 vaccines to protect against severe COVID-19.¶ To use all available data, this investigation included children and adolescents admitted through October 29, 2023, which included September 11, 2023-October 29, 2023, when children and adolescents were eligible to receive updated monovalent vaccines specific for the Omicron XBB lineage.However, no child or adolescent in this investigation had received an updated monovalent dose before the October 29, 2023, cutoff date.** Children and adolescents were enrolled from 34 hospitals in 26 states across all four U.S. Census Bureau regions.Northeast: Boston Children's Hospital (Massachusetts), Children's Hospital of Philadelphia (Pennsylvania), Cooperman Barnabas Medical Center (New Jersey), and Columbia University Irving Medical Center/New York-Presbyterian (New York); Midwest: Akron Children's Hospital (Ohio), Children's Hospital of Michigan (Michigan), Children's Mercy Kansas City (Missouri), Children's Nebraska (Nebraska), Cincinnati Children's Hospital Center (Ohio), C.S. Mott Children's Hospital (Michigan), Lurie Children's Hospital (Illinois), Mayo Clinic (Minnesota), Minnesota Masonic (Minnesota), Nationwide Children's Hospital (Ohio), and Riley Children's (Indiana); South: Arkansas Children's Hospital (Arkansas), Children's of Alabama (Alabama), Children's Healthcare of Atlanta, Emory University (Georgia), Children's Hospital of New Orleans (Louisiana), Children's Medical Center of Dallas (Texas), Holtz Children's Hospital (Florida), Medical University of South Carolina Children's Health (South Carolina), Monroe Carell Jr. Children's Hospital at Vanderbilt (Tennessee)

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