Safety & Immunogenicity of Enterovirus Type 71 Vaccine in Healthy Adults and Children 6-71months

Inclusion Criteria: * Bangladeshi healthy adults 18-45yrs and children aged 6-71 months on the day of screening; * Either sex; * The participant /parents or guardian of the participant properly informed about the study and having signed the informed consent form (ICF); * Participant/Parents' or guardian's availability for the entire period of the study and reachability by study staff for post-vaccination follow-up Exclusion Criteria: Exclusion Criteria for Inoculation of the First Dose: Whether the participant should be enrolled should be judged according to the following criteria. The participant cannot participate in the study if any of the following circumstances exists: 1. Previous history of hand, foot and mouth disease; 2. Allergy history to vaccine or components of the vaccine, previous history of asthma, serious adverse effects of the vaccine such as urticaria, dyspnea, angioneurotic edema or stomachache, etc; 3. Congenital malformation or developmental disorder, genetic defect, serious malnutrition, etc; 4. Autoimmune disease or immunodeficiency or immunosuppression; 5. Severe neurological disorders (epilepsy, convulsion or tic) or family history of mental disease; 6. History of thyroidectomy, or asplenia or functional asplenia; 7. Severely malnourished children 8. Abnormal coagulation functions (such as coagulation factor deficiency, blood coagulation disease and blood platelet disorders) or obvious bruise or blood coagulation disorders diagnosed by the doctors; 9. Received immunosuppressant therapy, cytotoxic drug therapy and inhaled corticosteroid therapy (excluding the corticosteroid aerosol therapy for allergic rhinitis and surface corticosteroid therapy for acute non-complicated dermatitis) in the past 6 months; 10. Received blood products within 3 months before receiving the investigational vaccine; 11. Received other study drugs or vaccines within 30 days before receiving the investigational vaccine; 12. Received live attenuated vaccines within 14 days before receiving the investigational vaccine; 13. Received subunit or inactivated vaccines within 7 days before receiving the investigational vaccine; 14. Various acute diseases or acute exacerbation of chronic diseases within 7 days; 15. Fever before vaccine inoculation, axillary temperature \>37.5°C; 16. Any other factors which are unsuitable for participation in the clinical trial as judged by the investigator. Exclusion Criteria for Inoculation of the Second Dose of Vaccine: 1. Any serious adverse event related to the inoculation of the investigational product; 2. Hypersensitivity after vaccine inoculation (including urticaria/rash appeared within 30 minutes after inoculation); 3. Any confirmed or suspected autoimmune disease or immunodeficiency disease, including human immunodeficiency virus (HIV) infection; 4. If acute or newly onset chronic disease occurs during vaccine inoculation; 5. The investigator judged that other significant reactions occur (including serious pain, serious swelling, serious activity limitation, continuous hyperthermia, serious headache or other systemic or local reactions); 6. The patient develops acute disease when vaccine is inoculated (acute diseases means the moderate or severe disease with or without fever); 7. Axillary temperature \>37.5°C when vaccine is inoculated; 8. The patient has received subunit inactivated vaccine within 7 days or live attenuated vaccines within 14 days.