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Influenza vaccine effectiveness and confounding factors among young children

Megumi Fujieda1, Akiko Maeda, Kyoko Kondo

  • 1Department of Public Health, Osaka City University Faculty of Medicine, Asahi-machi 1-4-3, Osaka 545-8585, Japan.

Vaccine
|June 25, 2008
PubMed

Insights

This study on influenza vaccine effectiveness in children under 6 found it reduced illness overall but wasn't proven in the youngest children (<2 years). Factors like age and daycare attendance influenced results.

Area of Science:

  • Pediatrics
  • Vaccinology
  • Epidemiology

Background:

  • Influenza poses a significant health risk to young children.
  • Assessing influenza vaccine effectiveness (IVE) in children under 6 years is crucial for public health strategies.
  • Confounding factors can impact the observed effectiveness of vaccines in pediatric populations.

Purpose of the Study:

  • To investigate the effectiveness of the influenza vaccine in children under 6 years of age during the 2002-2003 season.
  • To identify and analyze confounding factors that may influence influenza vaccine effectiveness estimates.
  • To determine if vaccine effectiveness differs across various pediatric age subgroups.

Main Methods:

  • A cohort study involving 2913 children (<6 years) from 54 pediatric clinics.
  • Weekly parental reporting of children's maximum body temperatures.
  • Logistic regression analysis to calculate adjusted odds ratios (ORs) for influenza-like illness (ILI).

Main Results:

  • Overall, influenza vaccination was associated with a reduced risk of ILI (OR: 0.76).
  • Younger age groups (<2.0 years and 2.0-3.9 years) had increased ILI risk compared to 4.0-5.9 year olds.
  • Significant vaccine effectiveness was observed in children aged 2.0-3.9 years (OR: 0.59) and 4.0-5.9 years (OR: 0.75), but not in those <2.0 years (OR: 1.07).
  • Factors like preschool attendance and having more siblings were associated with increased ILI risk.

Conclusions:

  • Influenza vaccination demonstrated effectiveness in children aged 2 years and older.
  • Vaccine effectiveness could not be demonstrated in children under 2 years of age.
  • Confounding factors such as age, daycare attendance, and family size should be considered when evaluating pediatric influenza vaccine effectiveness.

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