Phase Ⅱ Clinical Trial of 24-valent Pneumococcal Polysaccharide Conjugate Vaccine

Inclusion Criteria: * 1.Age and Identification: Volunteers aged ≥18 years on the screening day, able to provide valid legal identification. 2.Informed Consent: Volunteers who have received and understood the study information, voluntarily agreed to participate, and signed the Informed Consent Form. 3.Compliance: Volunteers able and willing to adhere to the clinical trial protocol requirements and attend all scheduled visits. Baseline Temperature: Axillary temperature ≤37.0°C on the enrollment day. Exclusion Criteria: * 5.Vaccination History: Prior receipt of pneumococcal conjugate vaccine; pneumococcal polysaccharide vaccine within the past 3 years; or a history of invasive Streptococcus pneumoniae disease. 6.Severe Allergic Reactions: History of severe allergic reactions, such as anaphylactic shock, allergic laryngeal edema, allergic purpura, thrombocytopenic purpura, local allergic necrotic reaction (Arthus reaction), etc. 7.Immunocompromised Status: Diagnosed congenital or acquired immunodeficiency; or receipt of systemic glucocorticoid therapy (e.g., prednisone or equivalent \>5 mg/day for ≥2 consecutive weeks) within 1 month prior to vaccination (local, inhaled, or nebulized steroids are permitted). 8.Severe Cardiovascular Diseases: History of arrhythmia, conduction block, myocardial infarction, or uncontrolled severe hypertension (on-site measurement: systolic blood pressure ≥160 mmHg and/or diastolic blood pressure ≥100 mmHg). 9.Acute Illness or Medication Use: Acute febrile illness, acute infectious disease, active cold symptoms, progressive influenza, or current use of related therapeutic medications. 10.Neurological/Developmental Disorders: History of neurological impairment, severe congenital malformation, severe developmental disorder, severe genetic defect, or severe malnutrition. 11.Neuropsychiatric History: Personal or family history of epilepsy, encephalopathy, or psychiatric disorders. 12.Coagulation Abnormalities: Diagnosed thrombocytopenia, coagulation dysfunction (e.g., coagulation factor deficiency, coagulation disorders, platelet abnormalities), or contraindications to intramuscular injection (e.g., anticoagulant therapy). 13.Splenic Abnormalities: Asplenia, functional asplenia, or splenectomy for any reason. 14.Uncontrolled Chronic Diseases: Severe chronic diseases or progressive conditions that cannot be stably controlled. 15.Blood Products/Immunoglobulins: Receipt of blood or blood products, or immunoglobulins within the past 3 months. 16.Live Attenuated Vaccines: Vaccination with live attenuated vaccines within the past 14 days. 17.Other Vaccines: Vaccination with other vaccines within the past 7 days. 18.Investigational Products: Receipt of other investigational drugs or vaccines within the past 1 month. 19.Concurrent Studies: Current participation or planned participation in another clinical study of drugs or vaccines during the research period. 20.Investigator's Discretion: Any other condition that, in the investigator's judgment, may interfere with study evaluation. 21.Additional Exclusions for Specific Populations: Females of Childbearing Potential (18-49 years): Positive urine pregnancy test on enrollment day; lactation; or planning to become pregnant within 6 months.