Safety and Immunogenicity of sIPV in Healthy Infants Aged 2 Months Following Sequential Immunization Program Combination with bOPV: A Phase 3, Randomized, Blinded, Parallel Positive-Controlled Clinical Trial

<b>Objectives</b>: This phase 3 clinical trial aimed to evaluate the safety and immunogenicity of the Sabin inactivated poliovirus vaccine (sIPV) manufactured by Biominhai in healthy infants following a sequential immunization regimen. <b>Methods</b>: A total of 300 healthy infants aged 2 months were randomly divided into the test group (sIPV-sIPV-bOPV) and the control group (wIPV-wIPV-bOPV) according to the ratio of 1:1. Both groups were inoculated under "2IPV + 1bOPV" schedule. Safety was assessed alongside poliovirus antibody levels before and after vaccination. <b>Results</b>: The overall incidence of adverse reactions (AEs) in the test and control groups was 44% and 39%, respectively. AEs in both groups primarily occurred following the first dose, with approximately 30% classified as grade 1 in severity. No significant differences were observed between groups regarding the incidence, severity, and symptoms of AEs. Additionally, no vaccine-related serious adverse events (SAEs) were reported. At 30 days after the last dose, the seroconversion rates of neutralizing antibodies against poliovirus types I and III reached 100% in both groups, while type II rates at 99% for the test group and 95% for the control. Notably, the seroconversion rates for all types in the test group were non-inferior to those in the control group. The geometric mean titers (GMTs) of neutralizing antibodies against poliovirus for type I (8622.64 vs. 2687.65), type II (207.73 vs. 54.06), and type III (2121.74 vs. 1699.12) were significantly higher in the test group (<i>p</i> < 0.0001 for type I and II; <i>p</i> = 0.04 for type III). <b>Conclusions</b>: The study concluded that the trial vaccine sIPV following sequential immunization program demonstrates good safety and immunogenicity, showing non-inferiority to the control vaccine.