Serological Survey on Monitoring the Positive Rate After Vaccination of Inactivated Polio Vaccine

Inclusion Criteria: * Healthy children who are regular residents in the pilot counties where the immune response is evaluated in pilot provinces. * Receiving the polio vaccination at 2, 3 and 4 months old with an interval of 28-35 days between doses according to national immunization schedule. The first dose of vaccine was administered at 2 full months old and less than 3 full months old. * No rotavirus vaccine was administered during the period of primary polio vaccinations, and no vaccines of category 2 (private market) were administered simultaneously with polio vaccine. If vaccines of category 2 other than rotavirus vaccine were administered, they should be administered with a space of at least 2 weeks with polio vaccination. Exclusion Criteria: * The first dose of polio vaccine was administered at more than 3 months old regardless of the reasons. * Children didn't get proper type and doses of vaccine as the protocal required. * Children with known immunodeficiency conditions. * Immunosuppressive agents or blood products were used after birth. * Vaccine contraindications.