Top 5 Takeaways

  1. Initial Vaccine Effectiveness: The original monovalent mRNA COVID-19 vaccine was 52% effective in preventing COVID-19-related hospitalization in children and adolescents when the last dose was received within 120 days prior to hospitalization.
  2. Decreased Protection Over Time: The effectiveness against hospitalization decreased to 19% when the last vaccine dose was administered between 120 to 364 days prior, highlighting the waning immunity over time.
  3. Effectiveness Against Critical Illness: Vaccine effectiveness against critical COVID-19-related illness, such as requiring mechanical ventilation or resulting in death, was higher at 57% if the last dose was received less than 120 days before hospitalization.
  4. Low Uptake of Updated Vaccines: There was a notably low frequency of children and adolescents who received updated COVID-19 vaccines, which emphasizes the need to increase coverage with the updated vaccinations.
  5. Public Health Implications: The findings support continued vaccination efforts, particularly with updated vaccine formulas, to maintain high levels of protection against COVID-19 hospitalizations and severe outcomes.

Original Article Author and Citation

Corresponding Author

Laura D. Zambrano,

Suggested Citation

Zambrano LD, Newhams MM, Simeone RM, et al. Durability of Original Monovalent mRNA Vaccine Effectiveness Against COVID-19 Omicron–Associated Hospitalization in Children and Adolescents — United States, 2021–2023. MMWR Morb Mortal Wkly Rep 2024;73(15):330–338. DOI:


The study analyzed the effectiveness of the original monovalent mRNA COVID-19 vaccine against hospitalization and severe illness in children and adolescents during the predominance of the Omicron variant, finding significant but waning protection over time.


The analysis utilized a case-control design across 34 sites in the Overcoming COVID-19 Network, comparing vaccinated and unvaccinated children hospitalized for COVID-19 or COVID-like symptoms.


The findings underscore the necessity of ongoing vaccination and booster doses, particularly with new vaccine formulations, to counter the reduced effectiveness of the original vaccines over time and the low current uptake rates.


To combat the decline in vaccine protection and low uptake of updated vaccines, public health recommendations strongly support keeping vaccinations up to date in children and adolescents to prevent severe COVID-19 outcomes.

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