Clinical Trial of PCV24 in Infants and Children Aged 2 Months to 5 Years

Inclusion Criteria: 1. Healthy infants who are aged 2 months (42-89 days), 7-11 months, 12-23 months, and 2-5 years; 2. The participants' guardian provides a legal identity document and the participants' vaccination record; 3. The participant's guardian understands and voluntarily signs the informed consent form; 4. Follow all study procedures and stay in contact during the study. Exclusion Criteria: 1. Received any pneumococcal vaccine prior to enrollment; 2. History of invasive pneumococcal diseases or other pneumococcal diseases caused by Streptococcus pneumoniae, as confirmed by laboratory tests; 3. History of severe adverse reactions to the vaccine or vaccine components, or history of allergy, such as urticaria, dyspnea, angioneurotic edema, anaphylactic shock; 4. Low birth weight (\<2.5kg), or premature infant (gestation weeks \< 37 weeks) (applies to infants younger than 12 months); 5. History of abnormal labor during delivery (planned cesarean section is excluded), history of asphyxia rescue and nervous system damage (applies to infants younger than 12 months); 6. Severe congenital malformations or developmental disorders, genetic defects, or malnutrition; 7. Have uncontrolled chronic diseases or history of severe diseases, including but not limited to cardiovascular diseases (e.g. congenital heart disease), hematological diseases (e.g. severe anemia), liver and kidney diseases, digestive diseases, respiratory diseases (such as active tuberculosis), malignant tumors and major functional organ transplantation history; 8. Autoimmune diseases, immunodeficiency diseases (including but not limited to systemic lupus erythematosus, rheumatoid arthritis, autoimmune thyroid disease, asplenia, functional asplenia, HIV infection); 9. Diagnosed abnormal blood coagulation function (eg, lack of blood coagulation factors, blood coagulopathy, abnormal platelet levels); 10. Have/have suffered from a serious neurological disorder (epilepsy or convulsions, but a febrile convulsion is not an exclusion criteria ) or mental illness, or have a family history of such diseases; 11. Consecutively received immunosuppressive therapy (excluding corticosteroid spray therapy for allergic rhinitis and surface corticosteroid therapy for acute non-concurrent dermatitis), or other immunoregulatory therapies, or cytotoxic therapy over 14 days within 6 months before vaccination, or plans to receive such therapies during the study; 12. Receipt of immunoglobulins or other blood products within 3 months prior to administration of the investigational vaccine (except for hepatitis B immunoglobulin or rabies immunoglobulin used within 1 month), or planned use of such products during the study period; 13. Received other investigational drugs or vaccines within 30 days prior to enrollment, or plan to receive such drugs or vaccines during the study; 14. Received live attenuated vaccine within 14 days prior to enrollment; 15. Received subunit or inactivated vaccine within 7 days prior to enrollment; 16. Acute diseases or acute onset of chronic diseases within 7 days prior to enrollment, known or potentially active infection; 17. Axillary temperature≥ 37.3 Degree Celsius before vaccination; 18. In the investigator's judgment, the participant has any other factors that make him or her unfit to participate in the clinical trial.