This study is a Phase IV, open, randomized, multi-center, controlled vaccine trial conducted in healthy Latin American infants, utilizing one or two supplemental doses of IPV in children previously vaccinated with 3 doses of bOPV. We will examine the impact of supplemental IPV on stool shedding and humoral immunity, as well as intra-IPV manufacturer comparability, and safety.

The world polio eradication effort is near its goal of reducing the number of new cases of polio to zero. However, final and definitive eradication of the disease will require stopping the use of oral polio vaccines (OPV's) which contain live virus and can rarely revert back to disease producing strains. This period will result in a risk of polio re-emergence as immunity will wane while some vaccine poliovirus will still be circulating. Inactivated polio vaccine (IPV) could potentially play a central role during this process but at present barriers of cost and logistics prevent its routine use in resource limited countries, and concerns exist as to whether IPV provides enough immunity in the intestine to reduce the spread of polioviruses in communities once OPV's are stopped. We plan a multi-center trial in Latin America in which we will administer 1 or 2 doses of IPV to children previously vaccinated with an OPV containing type 1 and 3 poliovirus (bOPV), and then assess the shedding in the stool of a type 2 OPV virus administered later. A decrease in the amount of virus shed compared to children not given IPV would indicate that the IPV boosted intestinal immunity, and would suggest that spread of virus in communities could be reduced using this strategy. We will also measure the impact of supplemental IPV's on antibody formation in the blood, which is a marker of protection of the individual from polio disease. A secondary aim will be to compare the immunogenicity and safety of three IPV's produced by different manufacturers. The overall goal will be to inform policy makers in polio eradication regarding the potential role that one or two doses of IPV might play in the final steps toward polio eradication.

Inclusion Criteria:

1. Age: 6 weeks (-7 to +14 days).
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 guardian as per country regulations

Exclusion Criteria:

1. Previous vaccination against poliovirus.
2. Low birth weight (BW <2,500 gm).
3. Multiple pregnancy (twins, triplets, etc.),
4. Any confirmed or suspected immunosuppressive or immunodeficient condition including human immunodeficiency virus (HIV) infection.
5. Family history of congenital or hereditary immunodeficiency.
6. Major congenital defects or serious uncontrolled chronic illness (neurologic, pulmonary, gastrointestinal, hepatic, renal, or endocrine).
7. Known allergy to any component of the study vaccines.
8. Uncontrolled coagulopathy or blood disorder contraindicating intramuscular injections.
9. Administration of immunoglobulins and/or any blood products since birth or planned administration during the study period.
10. Acute severe febrile illness at day of vaccination deemed by the Investigator to be a contraindication for vaccination.
11. Member of the subject's household (living in the same house or apartment unit) who has received OPV vaccine in the last 3 months.
12. Subject who, in the opinion of the Investigator or sub-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.