The Global Polio Eradication Initiative is on the brink of a major milestone. As of April, 2016, the serotype 2 component of oral poliovirus vaccine (OPV) will be removed from all immunisation activities worldwide. This transition, which is the first step in the synchronised withdrawal of all OPV serotypes, is essential to the polio endgame strategy. Although wild type 2 polioviruses have not caused a case of paralytic disease since 1999, vaccine viruses of this serotype have continued to cause rare cases of vaccine-associated paralytic poliomyelitis in OPV recipients or their close contacts,1 and sporadic emergences of circulating vaccine-derived polioviruses, wherein Sabin poliovirus strains mutate to regain neurovirulence.2

Preparations for the withdrawal of serotype 2 vaccine viruses have seen major shifts in routine immunisation practices across much of the world. To provide serotype 2 immunity by alternative means, more than 90 countries have introduced at least one dose of inactivated poliovirus vaccine (IPV) into their routine immunisation programmes since 2013.3 These efforts have laid the foundation for the replacement of trivalent OPV (tOPV) with a bivalent formulation targeting serotypes 1 and 3 (bOPV) in all routine and supplementary immunisation activities, after which serotype 2 OPV will be used only in a monovalent form if needed in an outbreak response.