The purpose of this study is to evaluate the immunogenicity and safety of sequential immunization schedules of Sabin IPV and bOPV.

A phase 4 clinical trial is designed to evaluate the safety and immunogenicity of different sequential immunization schedules of Sabin IPV and bOPV. To be specific, the subjects were divided into 3 groups.

Group 1 received Sabin-IPV+bOPV+bOPV respectively at the age of 2,3,4 months old.

Group 2 received Sabin-IPV+Sabin-IPV+bOPV respectively at the age of 2,3,4 months old.

Group 3 received Sabin-IPV+Sabin-IPV+Sabin-IPV respectively at the age of 2,3,4 months old.

Blood samples were collected before vaccination and 30 days after the third dose. Neutralization antibody against type I, Type II and Type III poliomyelitis virus were detected to evaluate the seroprotection rates and antibody geometric mean concentrations. The safety of the 3 immunization schedule groups were also monitored.

Inclusion Criteria:

• subjects aged from 60 days to 89 days old at the date of recruitment;
• with informed consent signed by parent(s) or guardians;
• parent(s) or guardians are able to attend all planned clinical appointments and obey and follow all study instructions;
• subjects did not receive any vaccination within 14 days;
• axillary temperature ≤37.0℃

Exclusion Criteria:

• allergic to any ingredient of vaccine or with allergy history to any vaccine;
• acute febrile disease or infectious disease;
• serious chronic diseases;
• any other factor that makes the investigator determines the subject is unsuitable for this study;