Safety, immunogenicity, and lot-to-lot consistency of a multidose Sabin strain-based inactivated polio vaccine: a phase III, randomized, blinded, positive-control clinical trial in infants aged 2 months

•The multidose Sabin strain-based inactivated polio vaccine (sIPV) showed good lot-to-lot consistency in immunogenicity.•The multidose sIPV met the noninferiority criteria of immunogenicity.•The multidose sIPV demonstrated a favorable safety profile.•No vaccine-related serious adverse events occurred. To evaluate the safety, immunogenicity, and lot-to-lot consistency of Sabin strain-based inactivated polio vaccine (sIPV) in a five-dose vial presentation. Stage I was an open-label safety observation, in which 72 healthy subjects (including 24 adults, children, and infants each) were given one or three doses of the five-dose vial sIPV; stage II was a randomized, blinded, and positive-control study, in which 1500 infants were randomized at the ratio of 1: 1: 1: 1: 1 into five groups to receive either three doses of the five-dose sIPV three lots, a conventional inactivated poliovirus vaccine, or a single-dose sIPV as controls, for primary immunization. Safety, immunogenicity, and lot-to-lot consistency were assessed. Among 1456 subjects who completed the primary immunization, the geometric mean titer ratios of types 1, 2, and 3 of each pair of lots were all within the equivalence criteria margin (0.67-1.50). The seroconversion rates of types 1, 2, and 3 in the combined test group were 98.02%, 94.07%, and 98.77%, respectively, which were noninferior to both control groups. The overall incidence of adverse reactions was 29.68% and erythema was the most common adverse reaction with incidences of 10.47%,9.33%, and 9.73% in the combined test group and control groups (P >0.05). The five-dose sIPV demonstrated good safety, immunogenicity, and lot-to-lot consistency.