A Phase III Clinical Trial of the Group A Meningococcal Polysaccharide Vaccine

* The First stage study (An early safety assessment study): * 18-50 years group: * Inclusion Criteria 1. Healthy adults aged 18 to 50 years. 2. Proven legal identity. 3. Participants should understand the contents of the informed consent form, the vaccine in this trial, voluntarily sign the informed consent form, and be capable of using thermometers, scales, and filling in diary cards and contact cards as required. 4. Participants should be able to communicate well with investigators, understand and comply with the requirements of this trial. 5. Axillary temperature ≤37.0℃. * Exclusion Criteria: 1. Contraindications for vaccination. 2. History of allergy to vaccines or drugs. 3. History of Epidemic Cerebrospinal Meningitis. 4. Immunization with any Group A meningococcal conjugate vaccine or polysaccharide vaccine within 12 months. 5. Immunization with any Group A and C meningococcal conjugate vaccine or polysaccharide vaccine within 3 years. 6. Immunization with any vaccine within 30 days. 7. Participants with convulsion, epilepsy, encephalopathy and psychiatric history or family history of epilepsy. 8. History of abnormal clinical manifestations and serious diseases to be excluded, including but not limited to nervous system, cardiovascular system, blood and lymphatic system, immune system, kidney, liver, gastrointestinal tract, respiratory system, metabolism, bones and other system diseases, and a history of malignant tumors. 9. Those who developed acute disease or acute attack of chronic disease. 10. Surgical removal of spleen or other important organs for any reason. 11. History of thrombocytopenia or other coagulation disorders may cause contraindication of subcutaneous injection. 12. Blood products such as immunoglobulin were received within 30 days before vaccination. 13. Have received immunosuppressive therapy or other immunomodulatory drugs within 6 months before signing the informed consent form (Note: inhaled or topical hormone drugs, except those with an interval of 14 days or more from the date of signing the informed consent form). 14. Those who participated in other clinical studies. 15. Participants who have a positive pregnancy test, or are breastfeeding, or plan to become pregnant, or plan to donate sperm or eggs from the screening to 12 months after the second vaccination. 16. Any other situations judged by investigators as not suitable for participating in this study. * 3-17 years group: * Inclusion Criteria 1. Healthy volunteer aged 3 to 17 years. 2. Proven legal identity. 3. Participants and their legal guardians should understand the contents of the informed consent form, the vaccine in this trial, voluntarily sign the informed consent form, and be capable of using thermometers, scales, and filling in diary cards and contact cards as required. 4. Participants and their legal guardians should be able to communicate well with investigators, understand and comply with the requirements of this trial. 5. Axillary temperature ≤37.0℃. * Exclusion Criteria: 1. Contraindications for vaccination. 2. History of allergy to vaccines or drugs. 3. History of Epidemic Cerebrospinal Meningitis. 4. Immunization with any Group A meningococcal conjugate vaccine or polysaccharide vaccine within 12 months. 5. Immunization with any Group A and C meningococcal conjugate vaccine or polysaccharide vaccine within 3 years. 6. Immunization with any vaccine within 30 days. 7. Participants with convulsion, epilepsy, encephalopathy and psychiatric history or family history of epilepsy. 8. Participant who has congenital heart disease, congenital malformation, Down's syndrome, sickle cell anemia or severe diseases with previous clinical manifestations that need to be excluded, including but not limited to nervous system, genetic defect disease (such as faba bean disease), cardiovascular system, blood and lymphatic system, immune system, kidney, liver, gastrointestinal tract, respiratory system, metabolism and bone system diseases, and History of malignant tumor. 9. Those who developed acute disease or acute attack of chronic disease. 10. Surgical removal of spleen or other important organs for any reason. 11. History of thrombocytopenia or other coagulation disorders may cause contraindication of subcutaneous injection. 12. Blood products such as immunoglobulin were received within 30 days before vaccination. 13. Have received immunosuppressive therapy or other immunomodulatory drugs within 6 months before signing the informed consent form (Note: inhaled or topical hormone drugs, except those with an interval of 14 days or more from the date of signing the informed consent form). 14. Those who participated in other clinical studies. 15. Women with positive pregnancy test after menarche. 16. Any other situations judged by investigators as not suitable for participating in this study. * 6-15 months group: * Inclusion Criteria 1. Healthy infants aged 6 to 15 months. 2. Proven legal identity. 3. Participants' legal guardians should understand the contents of the informed consent form, the vaccine in this trial, voluntarily sign the informed consent form, and be capable of using thermometers, scales, and filling in diary cards and contact cards as required. 4. Participants' legal guardians should be able to communicate well with investigators, understand and comply with the requirements of this trial. 5. Axillary temperature ≤37.0℃. * Exclusion Criteria: 1. Contraindications for vaccination. 2. History of allergy to vaccines or drugs. 3. History of Epidemic Cerebrospinal Meningitis. 4. Immunization with any Group A meningococcal conjugate vaccine or polysaccharide vaccine within 12 months. 5. Preterm birth at birth (before 37th week of pregnancy) or low birth weight (birth weight \< 2300g for girls and \< 2500g for boys); 6. They were vaccinated with live attenuated vaccine within 14 days before vaccination and subunit or inactivated vaccine within 7 days (copy of vaccination certificate of subjects); 7. Participants with convulsion, epilepsy, encephalopathy and psychiatric history or family history of epilepsy. 8. Participant who has congenital heart disease, congenital malformation, Down's syndrome, sickle cell anemia or severe diseases with previous clinical manifestations that need to be excluded, including but not limited to nervous system, genetic defect disease (such as faba bean disease), cardiovascular system, blood and lymphatic system, immune system, kidney, liver, gastrointestinal tract, respiratory system, metabolism and bone system diseases, and History of malignant tumor. 9. Those who developed acute disease or acute attack of chronic disease. 10. Surgical removal of spleen or other important organs for any reason. 11. History of thrombocytopenia or other coagulation disorders may cause contraindication of subcutaneous injection. 12. Blood products such as immunoglobulin were received within 30 days before vaccination. 13. Have received immunosuppressive therapy or other immunomodulatory drugs within 6 months before signing the informed consent form (Note: inhaled or topical hormone drugs, except those with an interval of 14 days or more from the date of signing the informed consent form). 14. Those who participated in other clinical studies. 15. Any other situations judged by investigators as not suitable for participating in this study. The Second stage study (A phase III clinical trial ) * Inclusion Criteria 1. Healthy infants aged 6 to 15 months. 2. Proven legal identity. 3. Participants' legal guardians should understand the contents of the informed consent form, the vaccine in this trial, voluntarily sign the informed consent form, and be capable of using thermometers, scales, and filling in diary cards and contact cards as required. 4. Participants' legal guardians should be able to communicate well with investigators, understand and comply with the requirements of this trial. 5. Axillary temperature ≤37.0℃. * Exclusion Criteria: 1. Contraindications for vaccination. 2. History of allergy to vaccines or drugs. 3. History of Epidemic Cerebrospinal Meningitis. 4. Immunization with any Group A meningococcal conjugate vaccine or polysaccharide vaccine within 12 months. 5. Preterm birth at birth (before 37th week of pregnancy) or low birth weight (birth weight \< 2300g for girls and \< 2500g for boys); 6. They were vaccinated with live attenuated vaccine within 14 days before vaccination and subunit or inactivated vaccine within 7 days (copy of vaccination certificate of subjects); 7. Participants with convulsion, epilepsy, encephalopathy and psychiatric history or family history of epilepsy. 8. Participant who has congenital heart disease, congenital malformation, Down's syndrome, sickle cell anemia or severe diseases with previous clinical manifestations that need to be excluded, including but not limited to nervous system, genetic defect disease (such as faba bean disease), cardiovascular system, blood and lymphatic system, immune system, kidney, liver, gastrointestinal tract, respiratory system, metabolism and bone system diseases, and History of malignant tumor. 9. Those who developed acute disease or acute attack of chronic disease. 10. Surgical removal of spleen or other important organs for any reason. 11. History of thrombocytopenia or other coagulation disorders may cause contraindication of subcutaneous injection. 12. Blood products such as immunoglobulin were received within 30 days before vaccination. 13. Have received immunosuppressive therapy or other immunomodulatory drugs within 6 months before signing the informed consent form (Note: inhaled or topical hormone drugs, except those with an interval of 14 days or more from the date of signing the informed consent form). 14. Those who participated in other clinical studies. 15. Any other situations judged by investigators as not suitable for participating in this study.