This is a randomized, observer-blinded Phase 2 study in healthy infants and toddlers 6-23 months of age at the time of the first vaccine dose.

The purpose of this study is to assess the safety and immunogenicity of the Vi-DT vaccine in age group 6-23months of age.

The Vi-DT vaccine is administered at 25 µg either as a single dose, or two doses given 6 months apart.

This study is carried out in healthy children aged 6 to 23 months at a single site. A total of 285 participants are enrolled, 114, 114 and 57 participants are randomized to either the single dose, two-dose Vi-DT regimens or placebo/comparator group, respectively within age strata. Three age strata is 6 to less than 9 months, 9 to 12 months and 13 to 23 months. The investigators allow the 9-12 months old children to receive Measles-Mumps-Rubella (MMR) vaccine concomitantly with Vi-DT vaccine and descriptive analysis of immune response to MMR only and to MMR and Vi-DT vaccines are performed to assess the possible immunological interference with MMR vaccine.

Inclusion Criteria:

• Healthy infants and children 6-23 months of age at enrollment as determined by medical history, physical examination and clinical judgment of the investigator
• Birth weight ≥ 2500 g
• ≥ 37 weeks of pregnancy or judge to be full-term by the midwife or birth attendant
• Parents aged 18 years and above and legal guardians aged 21 years and above as per the legal authorization in the Philippines, who have voluntarily given informed consent
• Parents/ legal guardians willing to follow the study procedures of the study and available for the entire duration of the study

Exclusion Criteria:

• Child with a congenital abnormality
• Subject with abnormal routine biological values at screening
• Subject concomitantly enrolled or scheduled to be enrolled in another trial
• Acute illness, in particular infectious disease or fever (axillary temperature ≥37.5°C), within three days prior to enrolment and vaccination
• Known history of immune function disorders including immunodeficiency diseases, or chronic use of systemic steroids (>20 mg/day prednisone equivalent for periods exceeding 10 days), cytotoxic or other immunosuppressive drugs
• Child with a previously ascertained or suspected disease caused by S. typhi
• Child who have had household contact with/and or intimate exposure to an individual with laboratory-confirmed S. typhi
• Known history or allergy to vaccines or other medications
• Know history of allergy to eggs, chicken protein, neomycin and formaldehyde
• History of uncontrolled coagulopathy or blood disorders
• Mother has known HIV infection or other immune function disorders
• Any abnormality or chronic disease which in the opinion of the investigator might be detrimental for the safety of the subject and interfere with the assessment of the study objectives
• Child whose parents or legal guardian planning to move from the study area before the end of study period

Observer Blinded