Booster Dose of sIPV Co-administered With MMR and HepA-I.

Inclusion Criteria: * (1) healthy toddlers aged 18 months (+4 months); * (2) completed three doses of sIPV primary immunization; * (3) completed one dose of MMR vaccination; * (4) able to provide proof of vaccination; * (5) able to provide legal proof of identity; * (6) The guardians of the participants were able to understand and agree to sign the informed consent. Exclusion Criteria: * (1) a history of vaccination with a polio-containing vaccine component in addition to three sIPV primary doses, according to the vaccination certificate; * (2) have received a second dose of MMR vaccine or a vaccine containing a vaccine for measles, mumps or rubella, or hepatitis A vaccine (inactivated or attenuated), according to the vaccination certificate; * (3) previous history of polio or measles or mumps or rubella or hepatitis A; * (4) known severe allergy to the vaccine or vaccine components, such as urticaria, dyspnea, angioedema; * (5) severe congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc.; * (6) with autoimmune diseases or immunodeficiency diseases (including but not limited to systemic lupus erythematosus, asplenia, functional asplenia, and HIV infection); * (7) abnormal coagulation function (such as coagulation factor deficiency, platelet abnormality), or obvious bleeding, hematoma, or ecchymosis after previous intramuscular injection or venipuncture; * (8) have/have had a serious neurological disease (e.g., encephalopathy, epile…