Implications of a Circulating Vaccine-Derived Poliovirus in Nigeria

Reversion of live attenuated oral poliovirus vaccine strains to a virulent phenotype is a rare but significant occurrence. In Nigeria, at least one vaccine-derived clone of type 2 poliovirus developed virulence, leading to ongoing transmission networks and many cases of paralysis. In this report, the characteristics of polio-associated disease and attack rates for this vaccine-derived clone are compared with circulating wild-type polioviruses 1 and 3. Increased vaccination efforts have significantly contributed to the control of all three serotypes. Implications for the global effort to eradicate polio are considered. In Nigeria, at least one vaccine-derived clone of type 2 poliovirus developed virulence, leading to ongoing transmission networks and many cases of paralysis. In this report, the characteristics of polio-associated disease and attack rates for this vaccine-derived clone are compared with circulating wild-type polioviruses 1 and 3. Since 1988, when the World Health Assembly resolved to eradicate poliovirus, the annual incidence of paralytic poliomyelitis has fallen by more than 99%. However, the annual number of cases reported for the years 2003 through mid-2009 has remained relatively constant, and continued transmission in endemic countries, especially Nigeria, led to a resurgence of re-infected countries across Africa from 2008 through 2009. 1 , 2 The emergence of a serotype 2 circulating vaccine-derived poliovirus (cVDPV) in Nigeria has complicated the epidemiology of polio as well as vaccine selection and scheduling for supplementary immunization activities. 3 A cVDPV is defined by the appearance of two . . .