Safety and Immunogenicity of a Vi-DT Typhoid Conjugate Vaccine

This is a Phase I, Randomized, observer-blinded, age de-escalating study.

The study objectives are:

1. To evaluate the safety of 25 μg of Vi-DT typhoid conjugate vaccine administered at 0 and 4 weeks.
2. To assess the immunogenicity of 25 μg of Vi-DT typhoid conjugate vaccine administered at 0 and 4 weeks.
3. To compare the safety and immunogenicity of Vi-DT and Vi-Polysaccharide typhoid vaccines.

This study will be carried out in healthy adults and children at a single site. Subjects will be stratified according to age.

The study procedure is as follows:

Visit 1 (day-1 to -7): Screen participants by medical history, physical examination and lab investigations. Collect blood for safety and immunogenicity assessments.

Visit 2 (day 0): Enroll, randomize and administer first dose of vaccine to eligible participants

Visit 3 (day 3): Assess participant safety by medical history and physical examination

Visit 4 (day 7): Record solicited adverse reaction 7 days post vaccination, and collect blood for safety lab assessments.

Visit 5 (day 28): Assess participant safety, collect blood for immunogenicity assessments, and administer second vaccine dose

Visit 6 (day 31): Participants safety will be assessed by medical history and physical examination

Visit 7 (day 35): Record solicited adverse reaction 7 days post second vaccination.

Visit 8 (day 56): Collect blood for immunogenicity assessments, assess participant safety, and fill in study completion form in the absence of any safety concern.

This study is observer-blind: vaccine administrator and vaccine safety evaluator will be two distinct persons to avoid bias of safety assessment. Trial staff other than the vaccine administrator.

Eligibility Criteria:
Inclusion Criteria:

1. Healthy male and female individual 2-45 years of age
2. Participants/Parents who have voluntarily given informed consent and/or assent.
3. Participants/Parents willing to commit complying with the study procedures of the investigator and available for the entire duration of study

Exclusion Criteria:

1. Participants concomitantly enrolled or scheduled to be enrolled in another trial
2. Acute illness, in particular infectious diseases or fever (axillary temperature \> 38°C), with in three days prior to enrollment and vaccination.
3. Known history of allergy to vaccines or other medications
4. Known history of allergy to egg, chiken protein, neomycin and formaldehyde.
5. History of uncontrolled coagulopathy or blood disorders
6. 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
7. Any abnormality or chronic disease which in the opinion of the investigator might be detrimental for the safety of the participant and interfere with the assessment of the trial objectives
8. Pregnancy \& Lactation (female adults)
9. Female with child-bearing potential during the study period. i.e., sexually active and not practicing effective acceptable contraceptive method
10. Individuals who have previously received any vaccines against typhoid fever
11. Individuals already immunized with any licensed vaccine within 4 weeks prior to enrolment/vaccination (day 0) and expected to receive other licensed vaccines within 60 days following the first dose (day 0), except for tetanus toxoid vaccine
12. Individuals who have a previously ascertained or suspected disease caused by S. typhi.
13. Individuals who have had household contact with/and or intimate exposure to an individual with laboratory-confirmed S. typhi
14. History of alcohol or substance abuse
15. Subject planning to move from the study area before the end of study period