Evaluation of Immunogenicity and Safety of Combined Immunization of sIPV, DTaP and MMR

Inclusion Criteria: * Subjects must have participated the clinical trial titled "Clinic Trial to Evaluate the Safety and Immunogenicity of Combined Immunization of sIPV and DTaP" (NCT04054882) in 2019, and have finished 3 doses of combined immunization of sIPV and DTaP; * Subjects aged 18 months old at the date of recruitment; * With informed consent form (ICF) signed by parent(s) or guardian(s); * Parent(s) or guardian(s) are able to attend all planned clinical appointments and obey/follow all study instructions; * Subjects have been vaccinated with a first dose of MMR, but have not been vaccinated with the 2nd dose of MMR and the booster (4th) dose of sIPV and DTaP; * No less than 14 days since the last dose of vaccination; * Axillary temperature ≤37.0℃. Exclusion Criteria: * With a medical history with hypersensitiveness, eclampsia, epilepsy, cerebropathia and neurological illness; * Allergic to any ingredient of vaccine or with allergy history to any vaccine; * Subjects with immunodeficency or suspected impairment of immunologic function (e.g. caused by HIV), or subjects are in the process of immunosuppressor therapy(Taking orally injecting of steroid hormone); * Administration of immunoglobulins within 30 days prior to this study; * Acute febrile disease(temperature ≥ 37.0°C) or infectious disease; * With a clearly diagnosed history of thrombocytopenia or other coagulopathy, may cause contraindications for subcutaneous injection; * With any serious chronic illness, acute infectious diseases, or respiratory diseases; * With severe cardiovascular disease, liver and kidney diseases or diabetes mellitus with complications; * With any kind of infectious, purulent, or allergic skin diseases; * With any other factor that makes the investigator determines the subject is unsuitable for this study.