Vaccine-Derived Polioviruses

The attenuated oral poliovirus vaccine (OPV) has many properties favoring its use in polio eradication: ease of administration, efficient induction of intestinal immunity, induction of durable humoral immunity, and low cost. Despite these advantages, OPV has the disadvantage of genetic instability, resulting in rare and sporadic cases of vaccine-associated paralytic poliomyelitis (VAPP) and the emergence of genetically divergent vaccine-derived polioviruses (VDPVs). Whereas VAPP is an adverse event following exposure to OPV, VDPVs are polioviruses whose genetic properties indicate prolonged replication or transmission. Three categories of VDPVs are recognized: (1) circulating VDPVs (cVDPVs) from outbreaks in settings of low OPV coverage, (2) immunodeficiency-associated VDPVs (iVDPVs) from individuals with primary immunodeficiencies, and (3) ambiguous VDPVs (aVDPVs), which cannot be definitively assigned to either of the first 2 categories. Because most VDPVs are type 2, the World Health Organization's plans call for coordinated worldwide replacement of trivalent OPV with bivalent OPV containing poliovirus types 1 and 3.