Active Surveillance of Adverse Events Following Influenza Immunization in Jiangsu Province, China: A 2019–2023 Retrospective Study

<b>Background:</b> Influenza vaccines have been administered in Jiangsu Province. This study aimed to conduct a comprehensive retrospective analysis of influenza vaccine safety in the region from 2019 to 2023. <b>Methods:</b> Data were sourced from the Chinese National Adverse Events Following Immunization Information System (CNAEFIS) and Jiangsu Provincial Electronic Immunization Registries System (JSEIRS) systems. A comprehensive retrospective analysis was performed to calculate the incidence rates of adverse events following immunization (AEFI) and to identify potential safety signals through disproportionality analysis. <b>Results:</b> Out of 4,906,905 administered doses, 2080 AEFI cases were reported, yielding an overall incidence rate of 42.39 per 1,000,000 doses. Significantly higher rates were observed in children aged 6-35 months (71.03 per 1,000,000) and among recipients of trivalent vaccines (52.79 per 1,000,000) compared to quadrivalent vaccines (36.03 per 1,000,000). The vast majority of AEFIs were mild, common adverse reactions (94.47%, predominantly fever and local reactions), occurring predominantly within one day post-vaccination, while disproportionality analysis identified expected signals for common adverse reactions and rare local purulent infections. <b>Conclusions:</b> Overall, the findings affirm the vaccine's favorable safety profile, align with pre-marketing data, and underscore the critical role of continuous post-marketing surveillance in maintaining public confidence and monitoring the safety of both established and new vaccine formulations.