Meningococcal vaccine for children 12–23 months old (Group ACYW135)

Inclusion Criteria:

1. Healthy participants aged 12 to 23 months.
2. The participant's legal guardian is capable of understanding and voluntarily signs the informed consent form.
3. Willing and able to comply with all scheduled visits, sample collection, vaccination, and other trial procedures.
4. Provision of legal identification documentation.

Exclusion Criteria:

1. History (or suspected history) of meningococcal disease.
2. History of infantile wheezing; history of allergy to the vaccine or any vaccine components (Group A/C/Y/W135 meningococcal capsular polysaccharide, mannitol, sucrose, sodium dihydrogen phosphate monohydrate, disodium hydrogen phosphate dodecahydrate, sodium chloride, water for injection), such as urticaria, dyspnea, angioedema; or other serious adverse reactions following prior vaccination.
3. Prior vaccination with Group A meningococcal polysaccharide vaccine with an interval ≤6 months since the most recent dose; prior vaccination with any other meningococcal vaccine other than Group A meningococcal polysaccharide vaccine (including but not limited to: Group A/C meningococcal polysaccharide/conjugate vaccine, ACYW135 meningococcal polysaccharide/conjugate vaccine).
4. Presence of autoimmune diseases or immunodeficiency diseases (including but not limited to asplenia, functional asplenia, HIV infection in the participant or the participant's mother).
5. Coagulation disorders (e.g., coagulation factor deficiency, platelet abnormalities) or history of significant bleeding, hematoma, or ecchymosis following intramuscular injection or venipuncture.
6. Presence of poorly controlled chronic diseases or history of serious illnesses, including but not limited to cardiovascular diseases, metabolic diseases, hematological diseases, hepatorenal diseases, gastrointestinal diseases, respiratory diseases, malignancies, or history of major organ transplantation.
7. Severe congenital anomalies, genetic defects, or malnutrition.
8. Presence of or history of severe neurological disorders \[epilepsy, convulsions or seizures\], or family history of psychiatric disorders.
9. Receipt of immunoglobulins or other blood products within the past 3 months, or planned receipt of such treatments during the study period.
10. Receipt of immunosuppressants or other immunomodulatory therapy for ≥14 days (e.g., prednisone ≥20 mg/day or ≥2 mg/kg/day, or equivalent), cytotoxic therapy within the past 6 months, or planned receipt of such therapies during the study period.
11. Receipt of any other investigational drug or vaccine within the past 3 months, or planned receipt during the study period.
12. Receipt of a live attenuated vaccine within the past 14 days, or receipt of a subunit or inactivated vaccine within the past 7 days.
13. Receipt of any other licensed vaccine within the past 28 days where administration at a different injection site from the study vaccine cannot be ensured.
14. Acute illness or acute exacerbation of chronic disease within the past 3 days, or known or suspected active infection.
15. Fever (axillary temperature \>37.0°C) on the day of scheduled study vaccination, or abnormal findings on physical examination that preclude vaccination.
16. Skin lesions, inflammation, ulcers, rash, or scarring at the intended injection site that may interfere with vaccination or local reaction assessment.
17. Any other condition that, in the investigator's judgment, makes the participant unsuitable for participation in this clinical trial.