The global poliomyelitis eradication initiative has been a tremendous success, with current evidence suggesting that wild poliovirus will cease to circulate anywhere in the world soon after the year 2000. As the goal of wild poliovirus eradication is approached, concern has been raised about the potential for persistent transmission of oral polio vaccine (OPV) viruses, as these viruses are known to revert toward wild-type neurovirulence. This paper has been extracted from a document prepared for the World Health Organization on the implications of OPV transmissibility for the strategy of stopping OPV vaccination after global eradication of wild polioviruses. The authors review the empirical evidence on OPV transmissibility available from household and community transmission studies and from mass-vaccination experiences. They then consider theoretical measures of transmissibility and persistence for wild and OPV viruses (secondary attack rate, basic reproduction number, and critical populations' size), to assess whether transmissibility of OPV viruses is sufficient to allow persistence of these viruses after cessation of vaccination. The findings indicate that OPV viruses could persist under various plausible circumstances, and that this potential should be a major consideration when planning the cessation of OPV vaccination.
PIP: In view of the growing concern over the potential for persistent transmission of oral polio vaccine (OPV) viruses, this paper examines a document on the implications of OPV transmissibility for the strategy of stopping OPV vaccination after global eradication of wild polio viruses. It reviews the empirical evidence on OPV transmissibility gathered from household and community transmission studies and from mass-vaccination experiences. It assesses whether transmissibility of OPV viruses are sufficient to allow persistence of these viruses after cessation of vaccination by considering theoretical measures of transmissibility and persistence for wild and OPV viruses. This review concludes that there is a risk that OPV viruses will persist and that such persistence could occur in a variety of ways. Further research is needed to assess the implications for OPV virus persistence, especially on issues concerning the long-term excretion by immunodeficient individuals; the ability for OPV viruses to spread and persist in communities with low seroprevalence; the risk of reversion to wild-type transmissibility; environmental survival and potential reservoirs of OPV virus; duration of mucosal immunity; and the prevalence of viable poliovirus in stored samples.