The purpose of this study is to assess the safety (serious adverse events [SAEs]), and severe adverse events [AEs] (grade 3 according to CTCAE 4.03) after one dose of SABIN tOPV in 1-5 year-old children and three doses of SABIN tOPV in 6 week-old infants, and immunogenicity (seroprotection rates for all 3 serotypes) 28 days after three doses of SABIN tOPV in vaccine-naïve infants.

This will be a single center, open study in children (aged 1 to 5 years) and vaccine-naïve infants, as follows: 50 OPV-vaccinated children aged 1 to 5 years to receive 1 dose of tOPV (Group 1); 104 vaccine-naïve infants to receive 3 doses of tOPV administered 28 days apart (Group 2)

Inclusion Criteria:

1. Age:

   Group 1- Children aged 1-5 years, previously vaccinated with ≥ 3 doses of OPV. Group 2- Infants aged 6 weeks (-7 to +14 days) with no previous polio vaccinations.

2. Healthy without obvious medical conditions that preclude the subject to be in the study as established by the medical history and physical examination.

3. Written informed consent obtained from 1 or 2 parents or legal guardians as per Dominican Republic regulations.

Exclusion Criteria:

1. Previous Vaccinations:

   Group 1: Previous vaccination against poliovirus outside of the national immunization schedule and any vaccine in the previous 4 weeks.

   Group 2: Any vaccination against poliovirus

2. Group 2: Infants with birth weight (BW) < 2,500 gm.

3. Any confirmed or suspected immunosuppressive or known immunodeficient condition including human immunodeficiency virus (HIV) infection.

4. Family history of congenital or hereditary immunodeficiency.

5. Major congenital defects or serious uncontrolled chronic illness (neurologic, pulmonary, gastrointestinal, hepatic, renal, or endocrine).

6. Known allergy to any component of the study vaccines or to any antibiotics.

7. Uncontrolled coagulopathy or blood disorder contraindicating intramuscular injections.

8. Administration of immunoglobulins and/or any blood products since birth or planned administration during the study period.

9. Acute severe febrile illness at day of vaccination deemed by the Investigator to be a contraindication for vaccination (the child can be included at a later time if within age window and all in/exclusion criteria are met).

10. Member of the subject's household (living in the same house or apartment unit) has received OPV in the last 3 months, or is scheduled to receive OPV during the study period.

11. Subject who, in the opinion of the Investigator, is unlikely to comply with the protocol or is inappropriate to be included in the study for the safety or the benefit-risk ratio of the subject.

3.5 months

Safety analyses were performed for solicited and unsolicited AEs by severity using the CTCAE version 4.03 published by NIH in 2010, as well as for SAEs and IMEs.