Effectiveness of 2023–2024 COVID-19 Vaccines in Children in the United States

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2023–2024 COVID-19 vaccines were recommended for individuals aged at least 6 months by the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices in September 2023.1 For children aged 6 months to 4 years, a multidose initial series (including 3 doses of Pfizer-BioNTech vaccine or 2 doses of Moderna vaccine) including at least one 2023–2024 dose was recommended for previously unvaccinated children; a single 2023–2024 dose was recommended for those with a complete initial series. For immunocompetent children aged at least 5 years, a single 2023–2024 dose was recommended, regardless of vaccination history.1 We estimated vaccine effectiveness (VE) of 2023–2024 mRNA COVID-19 vaccines in infants, children, and adolescents against COVID-19-associated emergency department and urgent care (ED/UC) encounters.The Virtual SARS-CoV-2, Influenza, and Other Respiratory Viruses Network (VISION) is a multisite electronic health record (EHR)-based system to estimate VE. VISION data are obtained from integrated medical and laboratory data; vaccination data are sourced from EHRs, immunization registries, and medical claims. Methods have been described previously.2–4 This analysis included immunocompetent children aged 9 months to 17 years across 7 VISION sites who visited a participating ED/UC between September 21, 2023, and August 22, 2024, with COVID-19-like illness (CLI; Supplemental Table 1) and were tested for SARS-CoV-2. Cases were encounters with a positive SARS-CoV-2 test result; controls had a negative test (Supplemental Methods). Nine months was the youngest age included to allow time for completion of the Pfizer-BioNTech initial series.Children aged 9 months to 4 years were considered to have received a 2023–2024 COVID-19 vaccine if at least one 2023–2024 mRNA COVID-19 vaccine dose was part of their initial series (eg, 2 prior doses and one 2023–2024 dose) or administered after an initial series composed of COVID-19 vaccines preceding the 2023–2024 vaccine (eg, 3 prior Pfizer doses [initial series] and any 2023–2024 dose). The 9 months to 4 years referent group was limited to children with a complete initial COVID-19 vaccine series with no receipt of a 2023–2024 dose or with no recorded COVID-19 vaccinations; children aged 9 months to 4 years with an incomplete primary series were excluded from analyses. Product-specific VE analyses for children 9 months to 4 years are described in the Supplement. For children aged 5 to 17 years, we compared those who received a single 2023–2024 COVID-19 vaccine dose to those who did not, regardless of COVID-19 vaccination history. VE was calculated using a test-negative design as (1− adjusted odds ratio [aOR]) × 100% where the aOR was calculated via multivariable logistic regression (Supplemental Methods).This activity was reviewed by CDC and participating site institutional review boards, and was conducted consistent with applicable federal law and CDC policy.The 45 316 eligible ED/UC encounters in children aged 9 months to 4 years included 1952 (4.3%) SARS-CoV-2 positive cases and 43 364 (95.7%) controls; 66 (3.5%) cases and 2004 (4.6%) controls received at least 1 dose of the 2023–2024 vaccine (Supplemental Table 2). Adjusted VE of 2023–2024 COVID-19 vaccine in children aged 9 months to 4 years was 35% (95% CI, 16% to 49%) in the 7 to 299 days after the most recent dose (median 89 days; Figure 1).The 57 771 eligible ED/UC encounters in children aged 5 to 17 years included 2150 (3.7%) SARS-CoV-2 positive cases and 55 621 (96.3%) controls; 79 (3.7%) cases and 3382 (6.1%) controls had received a 2023–2024 vaccine (Supplemental Table 2). Adjusted VE of the 2023–2024 COVID-19 vaccine in children aged 5 to 17 years was 44% (95% CI, 29% to 55%) in the 7 to 299 days after vaccination (median 108 days). VE did not vary substantially by age within the 5 to 17-year age group (Figure 1).Estimates stratified by time since vaccination for both age groups, and product-specific results among children aged 9 months to 4 years, are available in the supplemental materials and Figure 1.Within the VISION population, 2023–2024 COVID-19 vaccines provided children with substantial protection against COVID-19-associated ED/UC encounters. Like estimates of COVID-19 VE in other age groups5 and from previous seasons,3,6 we observed evidence of waning protection over time. Although VE estimates among children aged 9 months to 4 years differed by product, CIs overlapped.This analysis has limitations. First, low vaccine uptake resulted in imprecise VE estimates and could have led to biased estimates of VE. Second, while VISION data sources are robust, reliance on EHR data may result in underascertainment or misclassification of COVID-19 vaccination or case status. Third, prior SARS-CoV-2 infection was not accounted for, which may mediate subsequent COVID-19 and result in lower estimated VE. Finally, because this is an observational design, residual confounding is possible.Receipt of a 2023–2024 COVID-19 vaccine dose afforded immunocompetent children aged 9 months to 17 years additional protection against COVID-19–associated ED/UC encounters. Using several multisite networks, CDC continues to monitor the effectiveness of COVID-19 vaccines to inform policy decisions.CDC: Amanda Payne, PhD; Josephine Mak, MPH; Amber Kautz, PhD; Jennifer DeCuir, MD, PhD; Ruth Link-Gelles, PhD. Westat: Elizabeth Bassett, BA; Steph Battan-Wraith, PhD; Beyonce Carrington, MPH; Angela Cheung, MPH; Stan Chihuri, MPH; Jonathan M Davis PhD; Thomas Godwin, MPA; Melanie Goodrich, PhD; Nina Hamburg, MBA; Cassandra Hathaway, PhD; Salome Kayira, MPH; Lindsey Kirshner, MPH; Isaac Lartey, PhD; Victoria Lazariu, PhD; Yessie Martinez, MPH; Patrick Mitchell, ScD; Lawrence Reichle, MPH; Adriana Resendez, MPH; Anna Rukhlya, MA; Janet Watts, PhD; Sarah Wilson, MPH; Duck-Hye Yang, PhD; Adam Yates, PhD; and Yan Zhuang, PhD. Regenstrief: Ashley Wiensch, MPH, and Amy Hancock.

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