Immunogenicity, Safety and Immune Persistence of Sabin Strain Inactivated Poliovirus Vaccine: A Phase III Clinical Trial

The phased transition from oral poliovirus vaccine (OPV) to full-course immunisation with inactivated poliovirus vaccine (IPV) is a critical strategy for the global eradication of poliomyelitis. A randomised, double-blind, multi-centre, active-controlled clinical trial was conducted among healthy infants in China to evaluate the immunogenicity and safety of the Sabin strain IPV (sIPV). A total of 1260 healthy 2-month-old infants who had not previously received poliovirus vaccination were randomly assigned to receive three doses of either the investigational vaccine (sIPV) or the control vaccine (wIPV) according to a 0-, 28- and 56-day schedule, followed by a booster dose at 18 months of age. Per-protocol analysis (sIPV: n = 563; wIPV: n = 561) showed postprimary seroconversion rates for sIPV versus wIPV were: Type 1 (97.69% vs. 94.65%), Type 2 (98.22% vs. 87.70%) and Type 3 (99.82% vs. 98.57%). sIPV met noninferiority criteria (margin: -5%) for all serotypes, with one-sided 97.5% CI lower limits exceeding this margin. Postbooster geometric mean titre (GMT) for sIPV were 7297.40 (Type 1), 8490.51 (Type 2) and 7158.27 (Type 3), indicating robust immune memory. Safety profiles were similar overall, though sIPV had higher incidences of fever and hypersensitivity reactions. Serious adverse event rates were comparable (sIPV: 2.86% vs. wIPV: 2.70%). The study confirms sIPV's immunogenicity is noninferior to wIPV, with a potent booster response and acceptable safety. The trial was registered with chinadrugtrials.org.cn (CTR20170648).