Background: 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. Methods: 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. Results: 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. Conclusions: 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.

Objectives: Varicella is a highly contagious viral disease affecting children. The SV-1 cell line-based varicella attenuated live vaccine (SV-1VarV) is the first vaccine produced using the human diploid SV-1 cell substrate. This study evaluated the real-world safety of SV-1VarV among school-aged children in Jiangsu Province, China. Methods: A retrospective descriptive study was conducted using data from the Jiangsu Provincial Immunization Program Information System and the Chinese National Adverse Event Following Immunization Information System (CNAEFIS). Children aged 7–12 years who received SV-1VarV between July 2024 and March 2025 were included. The incidence, clinical characteristics, and demographic patterns of Adverse Events Following Immunization (AEFI) were analyzed. Reporting rates were calculated per 100,000 doses. Statistical analyses included chi-square tests, Cochran–Armitage trend tests, and Poisson regression analyses (α = 0.05). Results: A total of 366 AEFI cases were reported following 1,096,117 administered doses (33.4/100,000 doses), of which 364 were adverse reactions (33.2/100,000). General reactions accounted for 97.8% (mainly fever and local reactions), and abnormal reactions accounted for 2.2% (0.73/100,000). No serious adverse events or vaccine quality-related events occurred. Adverse reaction reporting rates declined with increasing age (p < 0.001) and were higher in males than females (36.7 vs. 29.2/100,000; p = 0.001). Poisson regression indicated that older age was independently associated with a lower risk of adverse reaction reporting, whereas sex and dose number were not significantly associated. Conclusions: SV-1VarV demonstrated a favorable safety profile during large-scale use in children aged 7–12 years. Most reactions were mild, self-limiting, and consistent with expected post-vaccination responses. These findings provide robust real-world evidence supporting the continued and expanded use of SV-1VarV in school-aged children to optimize varicella immunization strategies.

Background/Objectives: Varicella is a highly contagious childhood disease that may cause severe complications in susceptible populations. The SV-1 cell line-based varicella vaccine (VarV [SV-1]) has been increasingly used in routine immunization; however, safety and reporting patterns during the transition from partial use to full Expanded Program on Immunization (EPI) implementation remain poorly characterized. This study aimed to evaluate the safety profile and reporting dynamics of VarV (SV-1) before and after its incorporation into the Expanded Program on Immunization in Jiangsu Province, China. Methods: A retrospective observational study was conducted using data from the Jiangsu Provincial Immunization Integrated Service Management Information System and the Chinese National Adverse Event Following Immunization (AEFI) Information System (CNAEFIS), including all reported AEFI following VarV (SV-1) vaccination among children under 6 years of age during 2021–2023. Temporal trends, distribution characteristics, and factors associated with AEFI reporting were assessed using descriptive analyses, negative binomial (NB) regression models, and interrupted time series (ITS) analysis. Results: A total of 1,208,500 doses of VarV (SV-1) were administered, and 634 AEFI cases were reported, corresponding to an overall reporting rate of 52.46 per 100,000 doses. Most reported events were mild, self-limiting common reactions, predominantly pyrexia and injection-site reactions. No serious adverse events were identified. Although no immediate level change was observed at EPI implementation, a significant increasing post-EPI trend was detected, consistent with enhanced surveillance sensitivity rather than a change in intrinsic vaccine safety. Abnormal reactions were rare and resolved without sequelae. Conclusions: AEFI reporting rates following VarV (SV-1) vaccination in Jiangsu Province were within expected ranges, predominantly mild and reversible. Findings support the favorable safety profile of the VarV (SV-1) in routine childhood immunization programs and provide real-world evidence to support continued implementation of the two-dose varicella vaccination strategy within the EPI.