Adverse events following immunization among children with epilepsy: A self-controlled case series

Background: In children with epilepsy, fever and illness are known triggers for seizure; therefore, clinicians and parents could be concerned that immunization-induced inflammation and fever could also trigger seizures. We sought to estimate the risk of emergency department (ED) visit or hospitalization for epilepsy/seizure and all causes after immunization in children younger than 7 years of age with epilepsy. Methods: We conducted a self-controlled case series of children diagnosed with epilepsy before their 7th birthday and immunized from 2005 to 2015 in Ontario (population 14.2 million) and Manitoba (population 1.3 million), Canada, using administrative healthcare data. We estimated the age-and season-adjusted relative incidence (aRI) of epilepsy/seizure-related and all-cause ED visits/hospitalizations during various risk periods 0-28 days after inactivated and live immunizations versus a control period 35-83 days postimmunization. Estimates from each province were analyzed separately and then combined in a random-effects meta-analysis. Results: The combined risk of epilepsy/seizure-related hospitalization/ED visit was increased 0-2 days after inactivated vaccines (aRI = 1.5, 95% confidence interval: 1.1-1.9) and 7-10 days after live vaccines (aRI = 1.9, 1.4-2.7). For all-cause ED visit/hospitalization, the combined aRI estimate was 0.9 (0.8-1.2) 0-2 days after inactivated vaccines and 1.3 (1.1-1.5) 7-10 days after live vaccines. Conclusions: The risk of epilepsy/seizure-related ED visit/hospitalization was modestly increased among children with epilepsy during peak periods of fever and inflammation following inactivated and live vaccines. These risks must be balanced against the risk of complications from vaccine-preventable diseases.