The goal of this clinical trial is to evaluate the immunogenicity and safety of an investigational group ACYW135 meningococcal conjugate vaccine in healthy children aged 2 to 6 years.

The main questions it aims to answer are:

Is the immune response induced by the investigational vaccine non-inferior to that of the licensed control vaccine, as measured by serum antibody levels? What safety profile does the investigational vaccine have in this pediatric population? Researchers will compare the investigational vaccine group with the control group (licensed ACYW135 polysaccharide vaccine) to determine if the new vaccine provides comparable immune protection with an acceptable safety profile.

Participants will:

Receive a single dose of either the investigational vaccine or the control vaccine by intramuscular injection; Provide two blood samples (before vaccination and 30 days after) for antibody testing; Have their vaccination site and overall health monitored for AE/AR immediately after injection, for 7 days and for 30 days through diary card and follow-up contacts; Be followed for serious adverse events for 6 months after vaccination. A total of 660 participants will be enrolled and randomly assigned in a 1:1 ratio to either the investigational group or the control group.

Inclusion Criteria:

1. Healthy participants aged 2 to 6 years.
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/asthma; 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 or Group A/C meningococcal polysaccharide vaccine with an interval ≤1 year since the most recent dose; prior vaccination with any meningococcal polysaccharide/polysaccharide conjugate vaccine other than Group A or Group A/C meningococcal polysaccharide vaccines (including but not limited to: ACYW135 meningococcal polysaccharide vaccine, 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 systemic lupus erythematosus, ankylosing spondylitis, autoimmune thyroid disease, 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 (excluding history of febrile seizures)] or psychiatric disorders, or family history of psychiatric disorders.
9. Receipt of immunoglobulins or other blood products within 3 months prior to enrollment, or planned receipt of such treatments during the trial 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 6 months prior to enrollment, or planned receipt of such therapies during the study period.
11. Receipt of any other investigational drug or vaccine within 3 months prior to enrollment, or planned receipt during the study period.
12. Receipt of a live virus vaccine within 2 months prior to enrollment.
13. Receipt of influenza vaccine within 15 days prior to enrollment, or planned receipt of influenza vaccine within 15 days post-enrollment, or planned receipt of influenza vaccine between Days 16-28 post-enrollment at an injection site different from the study vaccine cannot be ensured.
14. Receipt of any other licensed vaccine (excluding live virus vaccines and influenza vaccine) within 1 month prior to enrollment, or planned receipt of any other licensed vaccine (excluding influenza vaccine) within 1 month post-enrollment.
15. Acute illness or acute exacerbation of chronic disease within 3 days prior to enrollment, or known or suspected active infection.
16. Fever (axillary temperature >37.0°C) on the day of scheduled study vaccination, or abnormal findings on physical examination that preclude vaccination.
17. Skin lesions, inflammation, ulcers, rash, or scarring at the intended injection site that may interfere with vaccination or local reaction assessment.
18. Any other condition that, in the investigator's judgment, makes the participant unsuitable for participation in this clinical trial.