Timeliness of signal detection for adverse events following influenza vaccination in young children: a simulation case study

OBJECTIVES: To determine how soon after commencement of the seasonal influenza vaccination programme, the AusVaxSafety active vaccine safety surveillance system, currently in use across Australia, would have detected a safety signal had it been operating in 2010 when there was an unprecedented number of febrile seizures in young children associated with one specific influenza vaccine brand, Fluvax (CSL Biotherapies). DESIGN: Simulation study. SETTING: Western Australian vaccine influenza coverage and adverse event surveillance data. OUTCOME MEASURES: Simulated solicited responses from caregivers who would have received an SMS survey about adverse events experienced following seasonal influenza vaccination of their children aged 6 months to <5 years. PARTICIPANTS: None. RESULTS: We estimated a >90% probability of a safety signal being detected by AusVaxSafety based on solicited reports for either fever or medical attendance at or before the week ending 28 March 2010, 3 weeks after the start of vaccine distribution. Suspension of the national paediatric influenza vaccination programme as a result of the passive adverse events surveillance operating at the time did not occur until 23 April 2010. CONCLUSIONS: Active vaccine safety surveillance leading to rapid detection of a safety signal would likely have resulted in earlier suspension of Fluvax from the vaccination programme, prevention of many febrile convulsions and maintenance of public confidence in influenza vaccination for young children.