Safety and Immunogenicity of Sabin Strain Inactivated Poliovirus Vaccine Compared With Salk Strain Inactivated Poliovirus Vaccine, in Different Sequential Schedules With Bivalent Oral Poliovirus Vaccine: Randomized Controlled Noninferiority Clinical Trials in China.

Background. A new Sabin strain inactivated poliovirus vaccine (sIPV) proved to be immunogenic and safe in all IPV primary immunization in the previous study, with the corresponding profiles in sequential immunizations unclear. Methods. Two clinical trials on the "IPV + 2 bivalent oral polio vaccine (2bOPV)" (Trial A) and "2IPV + bOPV" (Trial B) vaccination were conducted. Both clinical trials were randomized, controlled, double-blinded, noninferiority trials, and wild-strain IPV (wIPV) was adopted as the control vaccine. In each clinical trial, 240 healthy infants were enrolled and randomly assigned to receive sequential vaccinations containing sIPV or wIPV. Immunogenicity and safety were assessed using per-protocol and safety populations, respectively. Results. For Trial A, the seroconversion rates in the experimental and control groups were 100% and 99.1%, respectively, against type 1; both 100.0% against type 3. For Trial B, the seroconversion rates in experimental and control groups were 99.2% and 100.0%, respectively, against type 1; both 100% against type 3. No serious adverse events related to vaccines were reported. Conclusions. The new sIPV demonstrated an immunogenicity noninferior to that of the wIPV and a good safety profile in sequential vaccination with bOPV.