The goal of this clinical trial is to evaluate the protective efficacy of S. Flexneri-S. Sonnei bivalent conjugate vaccine against diarrhea caused by Shigella infection in infants and children aged 6 months to 5 years. Researchers will observe the incidence of diarrhea of any severity due to Shigella flexneri and Shigella sonnei infection 30 days after full immunization. The subjects will receive 2 doses of vaccination.

Inclusion Criteria:

• Infants and children aged 6 months to 5 years.
• Legal guardians voluntarily agree to participate in the study and sign an informed consent form.
• Legal guardians agree to comply with the requirements of the clinical trial protocol and are willing and able to participate in all planned follow-ups.
• The subject's guardian agrees that the subject should not abuse antibiotics. If needed，antibiotics should be used under the guidance of a doctor and avoid taking antibiotics on their own during the clinical trial.
• Based on medical history, physical examination, and the investigator's judgment, the subject is determined to be in good health.

Exclusion Criteria:

• History of confirmed bacterial dysentery in the past 6 months.

• Serious allergy to tetanus toxoid, history of severe allergies, fever above 39.5°C following previous vaccination with a prophylactic biological product.

• Currently suffering from serious intestinal diseases, symptoms of diarrhea, abdominal pain, or bloody purulent stools in the past 15 days.

• Diagnosed pathological jaundice currently.

• Confirmed diagnosis of thrombocytopenia or other coagulation disorders.

• Known or suspected immunological deficiencies (e.g., perianal abscesses indicating potential immune deficiency in infants and young children), long-term treatment (≥14 days) with immunosuppressants within half a year before vaccination (radiotherapy, chemotherapy, systemic corticosteroids ≥2 mg/kg/day, antimetabolites, cytotoxic drugs), or parents confirmed to have HIV infection.

• Receipt of immunoglobulins/blood products (except hepatitis B immunoglobulin) within 3 months before vaccination.

• Severe congenital anomalies (important organ function impairment), severe malnutrition, developmental disorders, severe hereditary diseases.

• Currently suffering from the following diseases:

  1. Severe liver or kidney diseases, cardiovascular diseases, malignant tumors, and other severe chronic diseases.
  2. Diagnosed serious infectious diseases, such as tuberculosis, viral hepatitis, etc.
  3. Severe asthma.
  4. Generalized rashes, dermatophytosis, skin suppuration, or blistering.
  5. Convulsions, epilepsy, encephalopathy, psychiatric disorders or family history of psychiatric disorders.

• Planning to participate or currently participating in other vaccine or drug clinical trials.

• Any condition that the investigators believe may affect the evaluation of the study.