The Phase II clinical trial of the 24-valent pneumococcal polysaccharide conjugate vaccine (RZ700) will be carried out in infants and young children aged 2 months (minimum 6 weeks) to 71 months. The purpose of this study is to evaluate the immunogenicity and safety of the 24-valent pneumococcal polysaccharide conjugate vaccine.

Inclusion Criteria:

• Healthy subjects aged 2 months (minimum 6 weeks) and 7-71 months, whose guardians can provide valid identification documents for both the subjects and themselves, as well as proof of their guardianship relationship.
• The guardians of the subjects voluntarily agree to their participation in this trial, sign the Informed Consent Form (ICF), and are willing to comply with all requirements of this clinical trial protocol.
• The guardians of the subjects have the ability to understand the trial procedures (non-illiterate).

Exclusion Criteria:

• Subjects who have received any type of pneumococcal vaccine prior to enrollment, plan to receive a pneumococcal vaccine during the trial, or have a history of invasive diseases caused by Streptococcus pneumoniae (confirmed by any clinical, serological, or microbiological method).
• Subjects with abnormal physical examination results that are deemed clinically significant by a clinician.
• Subjects with suspected or confirmed fever (axillary temperature ≥ 37.5℃) within 3 days prior to enrollment; or those with an axillary temperature ≥ 37.5℃ on the day before the first dose of vaccination.
• Subjects with a history of acute illness, acute exacerbation of chronic illness, systemic use of antibiotics or antiviral drugs within 3 days prior to the first dose of vaccination; or those who have taken antipyretic, analgesic, or antiallergic drugs (e.g., acetaminophen, ibuprofen, loratadine, cetirizine, etc.) within 3 days prior to the first dose of vaccination.
• Subjects with a history of allergy to any component of the study vaccine, any vaccine containing tetanus toxoid, or a previous history of severe allergy to any vaccine or drug (including but not limited to anaphylactic shock, allergic laryngeal edema, allergic purpura, immune thrombocytopenic purpura, local allergic necrotizing reaction, dyspnea, angioedema, etc.); or a previous history of the aforementioned severe adverse reactions following the use of any vaccine or drug.
• Subjects who have received inactivated vaccines, subunit vaccines, or recombinant vaccines within 7 days prior to enrollment; or live attenuated vaccines, adenovirus vector vaccines, etc., within 14 days prior to enrollment.
• Subjects who have received any other investigational drugs within 3 months prior to enrollment or plan to use them during the trial; those who have received whole blood, plasma, or blood products (e.g., immunoglobulin therapy) within 3 months prior to enrollment or plan to receive such treatments during the trial.
• Subjects with a history of thrombocytopenia, idiopathic thrombocytopenic purpura, or other coagulation disorders diagnosed by a hospital; or a history of receiving anticoagulant therapy.
• Subjects with a known current or past history of infectious diseases diagnosed by a hospital, such as active tuberculosis, hepatitis B, hepatitis C, HIV infection, etc.
• Subjects with known or suspected severe chronic diseases (e.g., liver and kidney diseases, malignant tumors, infectious or allergic skin diseases, hemolytic uremic syndrome); or those whose condition is in the progressive stage and cannot be stably controlled.
• Infants aged 2 months (minimum 6 weeks) and 7-11 months with abnormal birth weight (<2500g), abnormal gestational age (<37 weeks or >42 weeks), abnormal delivery (dystocia, instrumental delivery), or a history of asphyxia or neuroorganic damage.
• Infants aged 2 months (minimum 6 weeks) and 7-11 months with severe eczema or severe jaundice (grade 3 or above).
• Subjects with severe congenital malformations, developmental disorders, genetic defects, severe malnutrition, or severe chronic diseases (e.g., tetralogy of Fallot, tricuspid atresia, Down syndrome, sickle cell anemia, etc.).
• Subjects with neurological diseases or neurodevelopmental disorders (e.g., febrile convulsions, epilepsy, encephalopathy, focal neurological deficits, encephalomyelitis or transverse myelitis, Guillain-Barré syndrome); or a history of mental illness in the subjects themselves or their biological parents.
• Subjects with a history of congenital or acquired immunodeficiency, immunosuppression, or autoimmune diseases; or those who have received immunomodulatory therapy within 6 months (e.g., immunosuppressive doses of glucocorticoids [dosage reference: equivalent to prednisone ≥0.5mg/kg/day for more than 2 weeks], monoclonal antibodies, thymopeptides, interferons, etc.); or plan to receive such treatments from enrollment to 30 days after the last dose of vaccination. Topical medications (e.g., ointments, eye drops, inhalants, or nasal sprays) are permitted.
• Subjects with asplenia, functional asplenia, or asplenia/resplenectomy caused by any condition.
• Subjects whose guardians may be unable to comply with trial procedures, adhere to agreements, plan to permanently relocate from the region before the trial is completed, or be away from the local area for a long time during scheduled visits.
• Researchers believe that the subject has any other factors that make them unsuitable for participating in the clinical trial, such that continued participation cannot ensure the subject's maximum benefit.