Priming after Inactivated Poliovirus Vaccine: Implications for Polio Eradication

Progress toward polio eradication has shifted attention to developing and implementing the endgame strategies. The process of replacing oral poliovirus vaccine (OPV) with inactivated poliovirus vaccine (IPV) has begun, starting with the withdrawal of Sabin type 2 poliovirus from OPV in April 2016, and the simultaneous introduction of IPV in routine immunization schedules. The addition of a single dose of IPV to the bivalent type 1 and type 3 OPV (bOPV) schedule was recommended as a risk mitigation strategy to prevent paralytic disease due to poliovirus type 2. Single-dose IPV, however, is insufficient for inducing seroconversion in a majority of the vaccinees, despite immune priming ability. In this report we review studies that explore immune priming and memory conferred by single-dose IPV even in situations where seroconversion is not achieved, and discuss the current knowledge gaps and their implications for sustaining global polio eradication and for refining of the endgame strategies.