This is an age-descending, randomized, placebo-controlled trial that will evaluate the safety and immunogenicity of a Trivalent Salmonella conjugate vaccine (TSCV). The trial will proceed from adults, to children, to toddlers, and then to infants.

This is an age-descending, randomized, placebo-controlled trial that will evaluate the safety and immunogenicity of a Trivalent Salmonella conjugate vaccine (TSCV). The trial will proceed from adults, to children, to toddlers, and then to infants.

In Step 1A-D of the trial, participants will be randomized to receive a single dose of TSCV (Full-strength or Half-strength), Typbar-TCV, or placebo, first in adults, then in children 5 to 9 years of age, then children 24 to 59 months of age, and then 16 to 23 months of age.

Participants will be followed for 6 months. After a Data Safety Monitoring Board (DSMB) review of the safety data, the trial will proceed to Step 2A and 2B whereupon 12- to 16-month-old toddlers and infants 8- to 11-months of age will be similarly and simultaneously randomized. Participants will be followed for 6 months.

After another DSMB safety review, Step 3 will commence with simultaneous enrollment of 12- to 14-week-old and 16- to 18-week-old infants who will each receive a single dose of TSCV, TCV or placebo. Participants will be followed for 6 months.

After a third DSMB safety review and selection of the preferred TSCV formulation (Full-strength versus Half-strength) for further clinical development (a decision taken by the Sponsor, Manufacturer, and funder, while taking into consideration the recommendation of the DSMB), Step 4 will evaluate a two-dose regimen. Infants 12 to 18 weeks of age will be randomized to receive either two doses of TSCV (at Full-strength or Half-strength, based on results from Steps 1-3) or placebo followed by Typbar-TCV. The priming dose will be administered at enrollment and the booster at ~9, ~12, or ~15-17 months of age.

Participants will be followed until 6 months after the last study vaccination.

Note -- Whenever investigational products are intended to be administered at a scheduled Expanded Program on Immunization visit, they will always be given 2 weeks after the routine EPI vaccines. This will not only avoid interference with EPI vaccines but will provide a convenient contact point for potential recruitment of participants for the study.

Inclusion Criteria:

• Healthy individuals, female or male

• Age (all age ranges are inclusive)

  1. Step 1A: Adults 20-35 years of age
  2. Step 1B: Children, 5-9 years of age
  3. Step 1 C: Pre-school children, 24-59 mos. of age
  4. Step 1D: Older toddlers, 16-23 months of age
  5. Step 2A: Young toddlers, 12-16 months of age
  6. Step 2B: Older infants, 8-11 months of age
  7. Step 3: Young infants,12-14 weeks of age OR 16-18 weeks of age
  8. Step 4: Young infants, 12-18 weeks of age

• For potential pediatric participants, the parents must live within the catchment area of the clinical study facility at the time of the study vaccinations and must intend to continue to reside in the area for the duration of the study

• Adult subjects and parents/ guardians of pediatric subjects must have provided informed consent

• Infant and toddler subjects in Steps 2, 3, and 4 must have received their scheduled EPI vaccines at least 14 days prior to receiving a study product.

Exclusion Criteria:

• A history of documented hypersensitivity to any component of the Trivalent Salmonella Conjugate Vaccine or of Typbar-TCV™
• A history of previous vaccination with any licensed or experimental typhoid vaccine A known history of diabetes, tuberculosis, malignancy, chronic kidney disease, cardiac disease, liver disease, progressive neurological disorder, poorly controlled seizure disorder, or a terminal illness based on participant interview and review of screening laboratory results.
• Severe malnutrition: i.e., weight-for-length Z-score of less than - 3.
• Receipt of any other investigational intervention in the last 6 months
• Known HIV infection or other forms of immunocompromise
• Receipt of systemic immunosuppressive medication including systemic corticosteroids
• For Step 1A, for females of child-bearing potential, a positive pregnancy test at the time of enrollment.
• For Step 1B, any female child who has experienced menarche.
• Acute illness with or without fever (temperature >38.0oC) is a temporary exclusion criterion. Enrollment may be postponed until 3 days after the illness has resolved.
• Positive malaria test is a temporary exclusion criterion. Participant may be enrolled 3 days after completing treatment.
• Any condition determined by the investigators to be likely to interfere with evaluation of the vaccine, to be a significant health risk to the participant, or to make it unlikely that the participant would complete the study