A Phase 4, Randomized Study to Evaluate the Safety and the Humoral and Intestinal Immunogenicity of One or Two Additional Doses of Licensed Inactivated Polio Vaccines (IPVs) in Latin American Infants Previously Vaccinated With Bivalent Oral Polio Vaccines (bOPVs)

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.