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Vaccine effectiveness against laboratory-confirmed influenza in infants: A matched case control study

Lauren W Cochran1, Steven Black, Nicola P Klein

  • 1Stanford University School of Medicine, Stanford, CA, USA. lauren_cochran@alumni.brown.edu.

Human Vaccines
|September 22, 2010
PubMed

Insights

Influenza vaccination showed 76% effectiveness in infants during the 2005-2006 season when vaccine and virus strains matched. However, effectiveness was not significant in other seasons, indicating a need for further infant influenza vaccine studies.

Area of Science:

  • Pediatric Infectious Diseases
  • Vaccinology
  • Epidemiology

Background:

  • Influenza poses a significant health risk to infants, yet vaccine effectiveness estimates in this population vary widely.
  • Few studies have utilized laboratory confirmation for influenza diagnoses in infants, limiting the precision of previous effectiveness data.
  • The trivalent inactivated influenza vaccine is commonly administered to infants, but its efficacy requires robust evaluation.

Purpose of the Study:

  • To evaluate the effectiveness of the trivalent inactivated influenza vaccine against laboratory-confirmed influenza in infants aged 6 to 23 months.
  • To assess the impact of one versus two vaccine doses on influenza prevention in this age group.
  • To analyze vaccine effectiveness across multiple influenza seasons with varying strain match conditions.

Main Methods:

  • A case-control study design was employed using data from the Kaiser Permanente Northern California Medical Care Program (2003-2006).
  • Infants aged 6-23 months with laboratory-confirmed influenza (cases) were matched with controls based on birth month/year and zip code.
  • Conditional logistic regression was used to calculate vaccine effectiveness, adjusting for potential confounders like chronic medical conditions.

Main Results:

  • During the 2005-2006 season, when vaccine and circulating strains were well-matched, influenza vaccination demonstrated 76% effectiveness (95% CI: 37-91%).
  • No statistically significant vaccine effectiveness was observed during the 2003-2004 and 2004-2005 influenza seasons.
  • The study included 300 laboratory-confirmed influenza cases and 1,648 matched controls across three influenza seasons.

Conclusions:

  • Influenza vaccine effectiveness in infants can be substantial when vaccine and circulating strains are well-matched, as seen in the 2005-2006 season.
  • The lack of significant effectiveness in other seasons suggests that strain variability and match are critical factors for infant influenza vaccine efficacy.
  • Further research is warranted to optimize influenza vaccine strategies and improve protection for infants against this common infection.

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