Polio eradication: the OPV paradox

Abstract

Routine and mass administration of oral polio vaccine (OPV) since 1961 has prevented many millions of cases of paralytic poliomyelitis. The public health value of this inexpensive and easily administered product has been extraordinary. Progress of the Global Polio Eradication Initiative has further defined the value of OPV as well as its risk through vaccine-associated paralytic poliomyelitis (VAPP) and vaccine-derived polioviruses (VDPV). Although both are rare, once wild poliovirus transmission has been interrupted by OPV, the only poliomyelitis due to poliovirus will be caused by OPV. Poliovirus will be eradicated only when OPV use is discontinued. This paradox provides a major incentive for eventually stopping polio immunization or replacing OPV, but it also introduces complexity into the process of identifying safe and scientifically sound strategies for doing so. The core post eradication immunization issues include the risk/benefits of continued OPV use, the extent of OPV replacement with IPV, possible strategies for discontinuing OPV, and the potential for development and licensure of a safe and effective replacement for OPV. Formulation of an informed post eradication immunization policy requires careful evaluation of polio epidemiology, surveillance capability, vaccine availability, laboratory containment, and the risks posed by the very tool responsible for successful interruption of wild poliovirus transmission.

Role of environmental poliovirus surveillance in global polio eradication and beyond

“…Recent circulating VDPV (cVDPV) outbreaks have, however, raised concern that, under certain circumstances, especially following decreased OPV coverage [28], the OPV strains have the potential to cause sustained transmission and paralytic disease [29][30][31][32][33][34][35][36][37][38][39]. A widely held view is that IPV immunization does not effectively protect against PV replication in gut mucosa, and hence, a switch from OPV to IPV alone might result in a situation where OPV-derived viruses from the last period of use, from chronically infected persons, or imported from other locations, might be able to be transmitted.…”

Cross-neutralizing human anti-poliovirus antibodies bind the recognition site for cellular receptor

“…The latter continuously emerge from oral polio vaccine (OPV) and threaten sustainability of polio eradication, which will not be complete until OPV use is stopped (1). Besides circulating VDPVs that cause outbreaks of paralytic disease (2), there are also immunodeficiency-associated VDPVs continuously excreted by chronically infected patients with certain types of immune disorders (3), and VDPVs of unknown origin isolated from environmental samples, possibly also excreted by chronic shedders.…”

Polioviruses and other Enteroviruses

“…ENVS and AFP surveillance will be critically important during the end stage of eradication and post eradication for documenting eradication and ensuring very early detection of any reemergence. ENVS will be especially important for populations with high IPV vaccine coverage, since the ratio of AFP cases to asymptomatic infections would be orders of magnitude lower than for under-vaccinated populations (Hovi et al, 2012 Live attenuated polio vaccine can be transmitted from person-to-person, a trait considered advantageous when WPV infections were endemic, but which is now problematic as the eradication endgame approaches (Dowdle et al, 2003). Specifically, like wild poliovirus, the OPV genome evolves during circulation.…”