This is an Open-labeled, Randomized, Controlled Phase IV Clinical Trial to Evaluate the Immunogenicity and Safety of Booster Dose of Sabin Strain Inactivated Poliovirus Vaccine (Vero cell) (sIPV) Co-administered with Measles, Mumps, Rubella (MMR) Combined Live Attenuated Vaccine and Inactivated Hepatitis A (Hep-A) Vaccine.

The trial plans to enroll 960 infants aged 18 months (+4 months) who had completed three primary doses of sIPV vaccine and were assigned in a 2:2:2:1:1 ratio to four groups including trial group 1, trial group 2, control group 1, control group 2, control group 2, with informed consent from the participant's guardian. Trial group 1 receive one dose of sIPV co-administered with one dose of MMR vaccine. Trial group 2 receive one dose of sIPV co-administered with one dose of inactivated hepatitis A vaccine. Control group 1 receive one dose of sIPV, control group 2 receive one dose of MMR vaccine, and control group 3 receive one dose of inactivated hepatitis A vaccine. About 3.0 ml of venous blood will be collected from all participants before and 30 days after vaccination for antibody detection. Immediate reactions will be observed for 30 minutes after vaccination, and adverse events occured from 0 to day 30 after vaccination will be collected.

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, epilepsy, convulsions [other than febrile convulsions]) or psychosis, a family history of neurological disease or psychosis;
• (9) receiving immunosuppressive or other immunomodulatory therapy, cytotoxic therapy within the past 6 months, or planning to receive such treatment during the trial;
• (10) have received an immune globulin or other blood products within the past 6 months or plan to receive such treatment during the trial;
• (11) receipt of other investigational vaccines within 30 days before vaccination with the investigational vaccines;
• (12) receipt of live attenuated vaccine within 28 days before vaccination with the investigational vaccine;
• (13) receipt of subunit or inactivated vaccine within 7 days before vaccination with the investigational vaccine;
• (14) acute diseases or acute episodes of chronic diseases within the past 7 days;
• (15) Axillary temperature >37.0℃ if fever occurred before vaccination;
• (16) which are unsuitable for participation in the clinical trial as judged by the investigators.