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 caseecontrol 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 mucocutaneous 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 benefiterisk 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 <10% of children). This study supports the importance of the existing network of hospitals for the evaluation of signals relevant to new vaccines and drugs.