This study was conducted on the basis of "Safety Observation of Sabin Strain Inactivated Polio Vaccine (Vero Cell) on primary Immunization, Booster Immunization and Simultaneous Vaccination with Other Vaccines in Infants and Young Children(ID: PRO-sIPV-MA4001-JX). Blood samples were collected in about 200 qualified subjects 1-9 months after their last vaccination of sIPV. And immunogenicity of sIPV and other vaccines simultaneously administrated will be tested, the antibodies against enterovirus (including EV71、CA16、CA6 and CA10) will also be tested.

Inclusion Criteria:

• Participated in the previous study (ID: PRO-sIPV-MA4001-JX)
• Subjects in the Primay immunization group(aged 2-3 months) need to complete 3 doses of sIPV vaccination, and the simultaneous vaccination group DTaP needs to complete 3 doses of vaccination; the booster immunity group(aged more than 18 months) needs to complete sIPV vaccination, and the simultaneous vaccination group needs to complete the corresponding vaccination;
• There should be an interval of 1-9 months between the last dose of vaccination and the date of blood sample collection;
• The guardian of subjects need to agree to sign the informed consent form.

Exclusion Criteria:

• The interval between vaccination and blood collection is less than 1 month, or more than 9 months;
• Subjects were participating in other clinical studies of vaccines or drugs;
• Other conditions that make subjects unsuitable for participating in this study judged by investigator's

Subjects in the Primay immunization group(aged 2-3 months) need to complete 3 doses of sIPV vaccination, and the simultaneous vaccination group DTaP needs to complete 3 doses of vaccination; the booster immunity group(aged more than 18 months) needs to complete sIPV vaccination, and the simultaneous vaccination group needs to complete the corresponding vaccination