Update on vaccine-derived polioviruses--worldwide, January 2006-August 2007.

In 1988, the World Health Assembly resolved to eradicate poliomyelitis worldwide. Subsequently, the Global Polio Eradication Initiative of the World Health Organization (WHO) reduced the global incidence of polio associated with wild polioviruses (WPVs) from an estimated 350,000 cases in 1988 to 1,998 reported cases in 2006 and reduced the number of countries that have never succeeded in interrupting WPV transmission to four (Afghanistan, India, Nigeria, and Pakistan). However, because vaccine-derived polioviruses (VDPVs) can produce polio outbreaks in areas with low rates of Sabin oral poliovirus vaccine (OPV) coverage and can replicate for years in immunodeficient persons, enhanced strategies are needed to limit emergence of VDPVs and stop all use of OPV once WPV transmission is eliminated. This report updates a summary of VDPV activity published in 2006 and describes VDPVs detected during January 2006-August 2007.