A Phase Ia clinical trial of 24-valent pneumococcal conjugate vaccine (PCV24) developed by Sinovac Life Science Co., Ltd will be conducted in children aged 2-17 years. The objective of the study is to evaluate the safety and immunogenicity of Sinovac PCV24. The trial is a randomized, double-blind, controlled combined with open-label phase Ia clinical trial.

A phase Ia clinical trial of the study of 24-valent Pneumococcal Conjugate Vaccine (PCV24) developed by Sinovac Life Science Co., Ltd (Sinovac) will be conducted in Chinese children aged 2-17 years. The trial is a randomized, double-blind, controlled combined with open-label study. The objective of this study is to evaluate the safety and immunogenicity of PCV24 manufactured by Sinovac Life Science Co., Ltd. The active control vaccine for participants aged 2-5 years is the Prevenar13® manufactured by Pfizer.

A total of at least 114 participants will be enrolled, including 24 children aged 6-17 years and 90 children aged 2-5 years. Children aged 6-17 years will receive PCV24 formulation 1 and PCV24 formulation 2 in a 1:1 ratio. Children aged 2-5 years will receive PCV24 formulation 1, PCV24 formulation 2 and Prevenar13® in a 1:1:1 ratio.

Inclusion Criteria:

1. Healthy volunteers who are aged 2-17 years;
2. Participants and their guardians provide legal proof of identity, as well as vaccination record (for children aged 2-5 years);
3. Participants' guardians understand and voluntarily sign the informed consent form; participants aged 8-17 years sign the written assent;
4. Participants can 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 (IPDs) or other pneumococcal diseases caused by Streptococcus pneumoniae, as confirmed by laboratory tests;
3. History of allergy or adverse reactions to the vaccine or vaccine components, or history of allergy, such as urticaria, dyspnea, angioedema and anaphylactic shock;
4. Congenital malformations or developmental disorders, genetic defects (such as Down syndrome, thalassemia, or G6PD deficiency), severe malnutrition;
5. Have uncontrolled chronic diseases or history of severe diseases, including but not limited to cardiovascular diseases, such as cardiovascular diseases (e.g. congenital heart disease), metabolic diseases (such as diabetes), 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;
6. Autoimmune diseases or immunodeficiency diseases (including but not limited to systemic lupus erythematosus, rheumatoid arthritis, autoimmune thyroid disease, asplenia, functional asplenia, HIV infection)
7. Diagnosed abnormal blood coagulation function (eg, lack of blood coagulation factors, blood coagulopathy, abnormal platelets level), history of obvious bleeding, hematoma or bruising after intramuscular injection or venipuncture.
8. Have/have suffered from a serious neurological disorder (epilepsy or convulsions) or mental illness or have a family history of such diseases.
9. Long-term alcohol or drug abuse.
10. Have received > 14 days of immunosuppressive or other immunomodulatory therapy in the past 6 months, or cytotoxic therapy, or plan to receive such therapy during the study period.
11. Received immunoglobulin or other blood products within 3 months prior to enrollment, or plan to receive such treatment during the study period;
12. Received other investigational drugs or vaccines within 30 days prior to enrollment, or plan to receive such drugs or vaccines during the study;
13. Received live attenuated vaccine within 14 days prior to enrollment;
14. Received subunit or inactivated or other vaccine within 7 days prior to enrollment;
15. Acute diseases or acute onset of chronic diseases within 7 days prior to enrollment, or known or suspected active infection;
16. Women who are pregnant or breastfeeding (if applicable);
17. Abnormalities in clinical laboratory indicators that exceed reference range and are clinically significant.
18. Had fever (axillary temperature> 37.0℃) before vaccination;
19. In the investigator's judgment, the participant has any other factors that make him or her unfit to participate in the clinical trial.

Quadruple for children aged 2-5 years; open-label for children aged 6-17 years