Effectiveness and safety of the A-H1N1 vaccine in children: a hospital-based case-control study

Objective To verify whether vaccination against the A-H1N1 virus in the paediatric population was effective in preventing the occurrence of influenza-like illness (ILI) or was associated with adverse events of special interest. Design, setting and patients A case–control analysis was performed as part of surveillance of children hospitalised through the emergency departments of eight paediatric hospitals/wards for ILI, neurological disorders, non-infectious muco-cutaneous diseases and vasculitis, thrombocytopaenia and gastroduodenal lesions. Results Among 736 children enrolled from November 2009 to August 2010, only 25 had been vaccinated with the pandemic vaccine. Out of 268 children admitted for a diagnosis compatible with the adverse events of special interest, six had received the A-H1N1 vaccine, although none of the adverse events occurred within the predefined risk windows. Only 35 children out of 244 admitted with a diagnosis of ILI underwent laboratory testing: 11 were positive and 24 negative for the A-H1N1 virus. None of the A-H1N1 positive children had received the pandemic vaccine. The OR of ILI associated with any influenza vaccination was 0.9 (95% CI 0.1 to 5.5). Conclusions The study provides additional information on the benefit–risk profile of the pandemic vaccine. No sign of risk associated with the influenza A-H1N1 vaccine used in Italy was found, although several limitations were observed: in Italy, pandemic vaccination coverage was low, the epidemic was almost over by mid December 2009 and the A-H1N1 laboratory test was performed only during the epidemic phase (in
Article summary Article focus To assess the effectiveness of the influenza A-H1N1 vaccine and the occurrence of adverse events of special interest in the paediatric population. Key messages During the 2009–2010 influenza season, very limited information was available on the safety and effectiveness of the influenza A-H1N1 vaccine. Together with other post-marketing studies, our findings provide additional information on the benefit–risk profile of the pandemic vaccine. Strengths and limitations of this study The study focused on influenza-like illness and adverse events of special interest that were sufficiently severe to cause hospitalisation in children and provided additional information on the benefit–risk profile of the pandemic vaccine. A-H1N1 vaccination coverage in Italy during the 2009–2010 influenza season was very low, with around 4% of the general population and only 3.7% of the children included in this study having been vaccinated. The influenza outbreak was almost over by the first half of December 2009, and both the incidence and severity of the disease were lower than expected.