SARS-CoV-2 Epidemiology and COVID-19 mRNA Vaccine Effectiveness Among Infants and Children Aged 6 Months-4 Years - New Vaccine Surveillance Network, United States, July 2022-September 2023

MMWR Morb Mortal Wkly Rep. 2023 Dec 1;72(48):1300-1306. doi: 10.15585/mmwr.mm7248a2.


SARS-CoV-2 infection in young children is often mild or asymptomatic; however, some children are at risk for severe disease. Data describing the protective effectiveness of COVID-19 mRNA vaccines against COVID-19-associated emergency department (ED) visits and hospitalization in this population are limited. Data from the New Vaccine Surveillance Network, a prospective population-based surveillance system, were used to estimate vaccine effectiveness using a test-negative, case-control design and describe the epidemiology of SARS-CoV-2 in infants and children aged 6 months-4 years during July 1, 2022-September 30, 2023. Among 7,434 children included, 5% received a positive SARS-CoV-2 test result, and 95% received a negative test result; 86% were unvaccinated, 4% had received 1 dose of any vaccine product, and 10% had received ≥2 doses. When compared with receipt of no vaccines among children, receipt of ≥2 COVID-19 mRNA vaccine doses was 40% effective (95% CI = 8%-60%) in preventing ED visits and hospitalization. These findings support existing recommendations for COVID-19 vaccination of young children to reduce COVID-19-associated ED visits and hospitalization.

MeSH terms

  • COVID-19 Vaccines
  • COVID-19* / epidemiology
  • COVID-19* / prevention & control
  • Child
  • Child, Preschool
  • Hospitalization
  • Humans
  • Infant
  • Prospective Studies
  • RNA, Messenger
  • SARS-CoV-2 / genetics
  • United States / epidemiology
  • Vaccine Efficacy
  • Vaccines*


  • COVID-19 Vaccines
  • Vaccines
  • RNA, Messenger