Abstract
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.