No association between enterovirus 71 (EV71) vaccination and risk of febrile seizures: a population-based near real-time surveillance study.

BACKGROUND Since 2016, vaccines against enterovirus 71 (EV71) infection have been approved for use in China. Reports to the national passive surveillance system raised concerns about febrile seizures (FS) after EV71 vaccination. Rapid safety assessment of this novel vaccine is a public health priority. The objective was to assess risks of FS following EV71 vaccination in China. METHODS We used data from a Regional Health Information Platform in Ningbo. The exposed population was children aged 6-71 months who received any dose of EV71 vaccine from 1 January 2016 to 31 December 2019. We implemented a multilayered approach to actively monitor FS following EV71 vaccination that included near real-time surveillance using two complementary sequential designs and further signal evaluation performing self-controlled risk interval (SCRI) analyses. RESULTS A total of 330,668 EV71 doses were administered to the study population. During 157 weeks of sequential analyses, no statistically increased risks were detected, when compared with the self-matched control interval or the background risk. Further SCRI analyses confirmed no associations between EV71 vaccination and FS (adjusted incidence rate ratio: 1.04, 95% CI: 0.75 to 1.43). CONCLUSIONS Our results reassured the safety of FS after EV71 vaccination using postlicensure data for the first time.