Febrile seizures after 2010–2011 influenza vaccine in young children, United States: A vaccine safety signal from the vaccine adverse event reporting system

During the 2010–2011 influenza season, the Centers for Disease Control and Prevention and the Food and Drug Administration conducted enhanced vaccine safety monitoring for possible febrile seizures in all trivalent influenza vaccine (TIV) products in the United States using the Vaccine Adverse Event Reporting System (VAERS). We used Empirical Bayesian data mining techniques to assess disproportionate reporting after TIV and reviewed febrile seizure reports in children aged <5 years. On November 23, 2010, the combination of the coding term “febrile convulsion” and the Fluzone® TIV product exceeded a predetermined threshold in the VAERS database. By December 10, we confirmed 43 reports of febrile seizure following TIV in children aged 6–23 months. Clinical features of most reports were consistent with typical uncomplicated febrile seizures, and all children recovered. Further epidemiologic assessment of a possible association between TIV and febrile seizures was undertaken in a separate, population-based vaccine safety monitoring system.