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Live attenuated oral polio vaccine (OPV) and inactivated polio vaccine (IPV) are the tools being used to achieve eradication of wild polio virus. Because OPV can rarely cause paralysis and generate revertant polio strains, IPV will have to replace OPV after eradication of wild polio virus is certified to sustain eradication of all polioviruses. However, uncertainties remain related to IPV's ability to induce intestinal immunity in populations where fecal-oral transmission is predominant. Although substantial effectiveness and safety data exist on the use and delivery of OPV and IPV, several new research initiatives are currently underway to fill specific knowledge gaps to inform future vaccination policies that would assure polio is eradicated and eradication is maintained.

Globally, polio cases have reached an all-time low, and type 2 poliovirus (one of three) is eradicated. Oral polio vaccine (OPV) has been the primary tool, however, in rare cases, OPV induces paralysis. In 2013, the World Health Assembly endorsed the phased withdrawal of OPV and introduction of inactivated poliovirus vaccine (IPV) into childhood routine immunization schedules. Type 2 OPV will be withdrawn through a globally synchronized "switch" from trivalent OPV (all three types) to bivalent OPV (types 1 and 3). The switch will happen in 155 OPV-using countries between April 17(th) and May 1(st), 2016. Planned activities to reduce type 2 outbreak risks post-switch include the following: tOPV campaigns to increase type 2 immunity prior to the switch, monovalent OPV2 stockpiling to respond to outbreaks should they occur, containment of both wild and vaccine type 2 viruses, enhanced acute flaccid paralysis (AFP) and environmental surveillance, outbreak response protocols, and ensured access to IPV and bivalent OPV.

In 2013, the World Health Assembly endorsed a plan that calls for the ultimate withdrawal of oral polio vaccines (OPV) from all immunization programs globally. The withdrawal would begin in a phased manner with removal of the type 2 component of OPV in 2016 through a global switch from trivalent OPV to bivalent OPV (containing only types 1 and 3). To mitigate risks associated with immunity gaps after OPV type 2 withdrawal, the WHO Strategic Advisory Group of Experts has recommended that all 126 OPV-only using countries introduce at least one dose of inactivated polio vaccine into routine immunization programs by end-2015, before the trivalent OPV-bivalent OPV switch. The introduction of inactivated polio vaccine would reduce risks of reintroduction of type 2 poliovirus by providing some level of seroprotection, facilitating interruption of transmission if outbreaks occur, and accelerating eradication by boosting immunity to types 1 and 3 polioviruses.

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