Estimating influenza vaccine effectiveness using routine surveillance data among children aged 6-59 months for five consecutive influenza seasons

Objectives: We aimed to estimate the pooled vaccine effectiveness (VE) in children over five winters through data linkage of two existing surveillance systems. Methods: Five test-negative case-control studies were conducted from November to February during the 2004/2005 to 2008/2009 seasons. Sentinel physicians from the Viral Surveillance Network enrolled children aged 6-59 months with influenza-like illness to collect throat swabs. Through linking with a nationwide vaccination registry, we measured the VE with a logistic regression model adjusting for age, gender, and week of symptom onset. Both fixed-effects and random-effects models were used in the meta-analysis. Results: Four thousand four hundred and ninety-four subjects were included. The proportion of influenza test-positive subjects across the five seasons was 11.5% (132/1151), 7.2% (41/572), 23.9% (189/791), 6.6% (75/1135), and 11.2% (95/845), respectively. The pooled VE was 62% (95% confidence interval (CI) 48-83%) in both meta-analysis models. By age category, VE was 51% (95% CI 23-68%) for those aged 6-23 months and 75% (95% CI 60-84%) for those aged 24-59 months. Conclusions: Influenza vaccination provided measurable protection against laboratory-confirmed influenza among children aged 6-59 months despite variations in the vaccine match during the 2004/2005 to 2008/2009 influenza seasons in Taiwan. ? 2014 The Authors.