1. No increased risk of incident epilepsy was seen among children who received influenza vaccination during the 2009-2010 influenza season in Norway.
Evidence Rating Level: 2 (Good)
Study Rundown: Previous studies suggest associations between febrile seizures and influenza infection, complex febrile seizures and epilepsy, and seizures (particularly febrile) and vaccination (including influenza vaccination). However, a potential link between development of epilepsy and influenza vaccination is not defined. In this study, researchers investigated the possible association between a H1N1 pandemic influenza vaccine administered in Norway between October to December 2009 and incident epilepsy among children aged 0 to 17 years. Results showed the H1N1 vaccination for the 2009-2010 influenza season was not associated with an increased risk of epilepsy, even after adjusting for age-group, sex, and number of hospital or outpatient clinic visits in the during the year before the study. One limitation of this study was that it did not account for pre-existing comorbid conditions, which may have predisposed participants to epilepsy and increased their likelihood of being vaccinated. Results suggest that increased education may be warranted to ensure patients and families have a clear understanding of the risks and benefits of influenza vaccination.
Relevant reading: Pediatric neurologic complications associated with influenza A H1N1
In-depth [prospective cohort]: Researchers in this study analyzed data from 1 145 546 children (50.7% vaccinated, 48.7% female, 50.0% < 10 years old) seen in a Norwegian hospital or in outpatient clinic between October and December 2009. Using information from multiple, nationwide mandatory registries, study participants were observed for development of epilepsy (defined as 2 or more records from a care specialist coded with an epilepsy diagnosis) from October 2009 until December 2014. Investigators also applied a self-controlled case series analysis to determine the incidence rate ratio of epilepsy during several, pre-specified time periods after vaccination. During the study period, 3628 participants were diagnosed with epilepsy (incident rate: 6.09 per 10 000 person-years). Vaccinated children were more likely to be younger than 10 years old compared to 10-17 years (56.2% and 45.2%, respectively). No increased risk of incident epilepsy was appreciated following vaccination (HR 1.07, 95%CI 0.94 – 1.23). The study results did not change significantly after adjusting for sex, age-group and number of visits at health care facilities in the year before the study.
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