Lessons from the first year of the WAIVE study investigating the protective effect of influenza vaccine against laboratory-confirmed influenza in hospitalised children aged 6-59 months

Influenza Other Respir Viruses. 2010 Jul;4(4):231-4. doi: 10.1111/j.1750-2659.2010.00141.x.


Background: Influenza is major cause of paediatric hospitalisation. Influenza vaccine was offered to all children aged 6-59 months resident in Western Australia in 2008, and we wished to evaluate the effectiveness of this immunisation programme.

Objectives: To assess the practicalities of a nested matched case-control design to estimate the protective effect of inactivated influenza vaccination in hospitalised children aged 6-59 months.

Methods: Cases were hospitalised children with laboratory-confirmed influenza, while matched controls were recruited from children admitted for an acute non-respiratory illness. We estimated influenza vaccine effectiveness (VE) against influenza as 1--the adjusted odds ratio from multivariate logistic regression.

Results: The 2008 influenza season was characterised by a late peak and a predominance of influenza virus B. We recruited 26 hospitalised patients with laboratory-confirmed influenza and 50 matched controls. The proportion of cases who were fully vaccinated was 7% versus 30% of controls giving an adjusted VE of 83% (95% CI--54 to 98).

Conclusions: Recruiting sufficient controls was problematic and in the future, we will select controls hospitalised for an influenza-like-illness but influenza negative by laboratory PCR testing. The VE estimate was high but non-significant, reflecting the low number of cases.

MeSH terms

  • Age Factors
  • Case-Control Studies
  • Child, Preschool
  • Female
  • Hospitalization / statistics & numerical data*
  • Humans
  • Immunization Programs / methods*
  • Infant
  • Influenza A Virus, H1N1 Subtype / immunology
  • Influenza A Virus, H1N1 Subtype / isolation & purification
  • Influenza A Virus, H3N2 Subtype / immunology
  • Influenza A Virus, H3N2 Subtype / isolation & purification
  • Influenza B virus / immunology
  • Influenza B virus / isolation & purification
  • Influenza Vaccines / administration & dosage*
  • Influenza Vaccines / immunology
  • Influenza, Human / epidemiology*
  • Influenza, Human / immunology
  • Influenza, Human / prevention & control*
  • Influenza, Human / virology
  • Logistic Models
  • Male
  • Odds Ratio
  • Program Evaluation*
  • Treatment Outcome
  • Western Australia / epidemiology


  • Influenza Vaccines