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.

Background/Objectives: Sabin-strain inactivated poliovirus vaccine has been increasingly incorporated into routine immunization programs as part of the global strategy to eradicate poliomyelitis. As childhood immunization schedules become more complex, concerns persist regarding the safety of concomitant vaccination. Although randomized controlled trials and regional surveillance studies have demonstrated acceptable safety profiles, additional population-based real-world evidence remains valuable for evaluating the safety of sIPV administered concomitantly with other vaccines under routine programmatic conditions. Methods: A retrospective observational study was conducted using vaccination records and adverse events following immunization surveillance data collected in Liaoning Province, China, between 1 January 2022 and 30 June 2025. All reported adverse events following immunization following Sabin-strain inactivated poliovirus vaccine administration were extracted from the Chinese National AEFI Surveillance System. The reporting rates were calculated per 100,000 administered doses. Multivariable Poisson regression models with robust variance estimation were used to estimate adjusted rate ratios and 95% confidence intervals comparing standalone and concomitant sIPV administration, adjusting for sex, age in months, dose number, and city. Interaction analyses between vaccination mode and dose number were additionally performed. Results: A total of 205,576 sIPV doses were administered, including 144,724 doses administered alone and 60,852 doses administered concomitantly with other vaccines. Fifty-six adverse events following immunization were reported, corresponding to an overall reporting rate of 27.24 per 100,000 doses. Most reported adverse events following immunization were general reactions (91.07%), and all occurred within seven days after vaccination. The reporting rates for sIPV administered alone and concomitantly were 26.26 and 29.58 per 100,000 doses, respectively, with no significant difference between groups (p = 0.7869). After adjustment, concomitant sIPV administration was not associated with an increased risk of adverse events following immunization compared with standalone administration (adjusted rate ratios = 1.13, 95% confidence intervals: 0.59–2.16). No significant interaction between vaccination mode and dose number was identified. Conclusions: Sabin-strain inactivated poliovirus vaccine demonstrated a favorable safety profile when administered either alone or concomitantly with other vaccines. These findings support the continued use of flexible and synchronized vaccination strategies involving Sabin-strain inactivated poliovirus vaccine in routine immunization programs.