An open label study to evaluate immunogenicity, safety, and reactogenicity of Rotavac® (live attenuated oral rotavirus vaccine) as a 3-dose series in healthy infants aged between 6 weeks and 8 weeks in Vietnam

• The study is an open labeled, clinical trial in infants 6-8 weeks of age will be assigned to receive 3 doses of Rotavac® to evaluate the immunogenicity and safety.
• Active surveillance will be conducted for all participants for 14 & 28 days after each dose of vaccine to obtain information on adverse events. ("Reactogenicity")
• Childhood vaccines including pentavalent (Diptheria, Tetanus, Pertussis, Hib, Hepatitis B) and oral polio vaccine as well as injectable polio vaccine will be administered along with the study vaccines as per Expanded Program on Immunization (EPI)
• Safety assessments will include observation in the study clinic for 30 minutes after each vaccine administration to record immediate adverse events. A subject diary card and personal contact with the subjects will be made to record adverse events during the 14-day period following vaccine administration.

Inclusion Criteria

1. Healthy infants as established by medical history and clinical examination
2. Age: 6-8 weeks
3. Weight ≥2.5kgs at birth
4. Infants receiving EPI vaccines as per Vietnam immunization program
5. Parental ability and willingness to provide informed consent.
6. Parent who intends to remain in the area with the participant during the study period.

Exclusion Criteria:

1. Presence of diarrhea or vomiting in the previous 72 hours or on the day of enrollment (temporary exclusion).
2. Presence of fever (>37.5C) or hypothermia (<35.5C) on the day of enrollment (temporary exclusion).
3. Concurrent participation in another clinical trial.
4. Presence of significant malnutrition or any systemic disorder (cardiovascular, pulmonary, hepatic, renal, gastrointestinal, haematological, endocrine, immuno-logical, dermatological, neurological, cancer or autoimmune disease) as determined by medical history and/or physical examination which would compromise the child's health or is likely to result in non-conformance to the protocol.
5. History of congenital abdominal disorders, intussusception, abdominal surgery
6. Known or suspected impairment of immunological function based on medical history and physical examination.
7. Prior receipt of rotavirus vaccine.
8. A known sensitivity or allergy to any components of the study vaccines.
9. Major congenital or genetic defect.
10. Participant's parents not able, available or willing to accept active follow-up by the study staff.
11. Has received any immunoglobulin therapy and/or blood products since birth or planned administration during the study period.
12. History of chronic administration (defined as more than 14 days) of immunosuppressant including corticosteroids. Infants on inhaled or topical steroids may be permitted to participate in the study.
13. History of any neurologic disorders or seizures.
14. Any medical condition in the parents/ infants that, in the judgment of the investigator, would interfere with or serves as a contraindication to protocol adherence or a participant's parent's/legally acceptable representative's ability to give informed consent.