Polio End-game Strategies - Poliovirus Type 2 Challenge Study

Overview

Poliomyelitis eradication has entered its last phase with only three remaining endemic countries, of which Pakistan is one. There hasn't been a case of wild type poliovirus 2 since 1999, and no case of wild type poliovirus 3 since November 2012. However, paralytic polio resulting from circulating strains of Sabin poliovirus type 2 have become a challenge, and reported from several areas with low population immunity to polio, including in Pakistan. This study will provide data to National Immunization Authorities in order to make strategic decisions about their polio vaccination schedules in anticipation of the global tOPV to bOPV switch and will provide data on the proposed responses to type 2 poliovirus outbreaks.

The "Polio Endgame Strategy" consists of set of tasks and activities that will be implemented in the next five years. It includes gradual withdrawal of the widely used oral poliomyelitis vaccine (OPV) containing live poliovirus, and will eventually lead to complete eradication and containment of all wild, vaccine-related (VDPV) and Sabin polioviruses. The withdrawal of the type 2 components of trivalent OPV (tOPV) is the key component in the elimination of cVDPVs. This entails strengthening of the immunization system by introducing at least one dose of affordable IPV into the routine immunization schedule globally and then replacing the trivalent OPV with bivalent OPV in all OPV-using countries - setting the stage for eventually ending bOPV use in 2019-2020. Most of the developing countries have an OPV schedule however many developed and European countries follow the IPV only schedule. The current recommendations for polio eradication and endgame is IPV vaccine to be administered together with third OPV dose, which in most countries occurs at 14 weeks of age. This study will assess the protection to type 2 poliovirus achieved after completion of the recommended schedule with bOPV and IPV; it will compare immunogenicity of bOPV + IPV schedule with tOPV only schedule; and will quantify the cross-reactivity of bOPV on inducing type 2 immunological reaction. In addition, it will also provide first data on the proposed outbreak response to type 2 (either with mOPV 2 or with a combination of mOPV 2 and IPV 2). This study will provide data to National Immunization Authorities in order to make strategic decisions about their polio vaccination schedules in anticipation of the global tOPV to bOPV switch and will provide data on the proposed responses to type 2 poliovirus outbreaks.