Use of mOPV1 in Routine Immunization in Pakistan.

Pakistan has uninterrupted circulation of polioviruses and this may threaten the entire global community. Bivalent OPV (bOPV), which protects against types 1 and 3, is used for routine immunization. However, type-3 wild poliovirus is on the verge of eradication, therefore mOPV1 is important to achieve eradication of type-1 poliovirus. The main rationale of the study is to interrupt WPV1 circulation and stopping the outbreaks of VDPVs with the help of mOPV1 instead of bOPV2 for routine immunization, which contains live poliovirus, and will eventually lead to complete eradication and containment of type 1 WPV, vaccine-related (VDPV) and Sabin polioviruses. This study will provide data to National Immunization Authorities in order to make strategic decisions about their polio vaccination schedules in anticipation of the potential global bOPV2 to mOPV1 switch and will provide data on the proposed responses to type 1 poliovirus outbreaks.

Wild Polio Virus 1 (WPV1) is the only responsible virus for wild polio cases across the globe. The world has successfully eradicated wild poliovirus (PV) 2 and 3. Poliomyelitis eradication has entered its last phase with only three remaining endemic countries, of which Pakistan is one and has highest number of WPV1 cases in 2019. The main stream strategies by the Global Polio Eradication Initiative has made the substantial progress towards the eradication of poliomyelitis ever since the World Health Assembly has sanctioned it as an emerging global Public Health threat. These strategies focus on high-quality immunization activities (routine and supplemental) that target children from birth to age 5 years with oral poliovirus vaccines (OPVs), and maintaining a system for acute flaccid paralysis surveillance. Pakistan has uninterrupted circulation of polioviruses and this may threaten the entire global community and implies impending failure of goal of global eradication. According to the Polio endgame strategy 2019-2023, Pakistan and Afghanistan are the only countries in which WPV transmissions continues to be reported. The genetic sampling and environmental surveillance have revealed that WPV1 has predominantly persisted in Pakistan and Afghanistan and are closely linked as they constitute one epidemiological block. Bivalent OPV (bOPV), which protect against types 1 and 3, is used for routine immunization. However, type-3 wild poliovirus is on the verge of eradication, therefore mOPV1 is important to achieve eradication of type-1 poliovirus whose appearance has been continually been confirmed by the genetic and environmental samplings. The main rationale of the study is to interrupt WPV1 circulation and stopping the outbreaks of VDPVs with the help of mOPV1 instead of bOPV2 for routine immunization, which contains live poliovirus, and will eventually lead to complete eradication and containment of type 1 WPV, vaccine-related (VDPV) and Sabin polioviruses. The study rationale is in line with the Goal 1- Eradication of GPEI. This study will provide data to National Immunization Authorities in order to make strategic decisions about their polio vaccination schedules in anticipation of the potential global bOPV2 to mOPV1 switch and will provide data on the proposed responses to type 1 poliovirus outbreaks. Research Questions and Main Objectives : Overall Objectives of the study will be: * To assess the serum immunity against type 1,2 and 3 polioviruses achieved with two different mOPV1 routine immunization schedule (mOPV1+fIPV (fractional dose intradermal IPV); mOPV1+FIPV (full dose intramuscular IPV)) * To compare the serum immunity against type 1,2 and 3 polioviruses achieved with two different mOPV1 routine immunization schedule with bOPV2 routine immunization schedules (mOPV1+fIPV, mOPV1+FIPV with bOPV2+fIPV, bOPV2+FIPV) * To assess the type 2 response after One full dose IPV with mOPV1 and bOPV2 routine immunization schedule * To assess the type 2 response after two fractional doses of IPV with mOPV1 and bOPV2 routine immunization schedule