Although widespread use of trivalent oral poliovirus vaccines (tOPVs) has contributed to a reduction of 3 types of wild poliovirus (WPV), communities with low vaccination coverage can experience vaccine-derived polioviruses (VDPVs), according to a study in the CDCs Morbidity and Mortality Weekly Report.
Among the 721 reported patients with polio attributed to circulating VDPVs (cVDPVs) detected between January 2006 and May 2016, type 2 (cVDPV2s) accounted for more than 94%, according to the study. To address the risk of VDPV, a bivalent OPV (bOPV) – containing only types 1 and 3 attenuated polioviruses – has been developed, removing OPV type 2 from all immunization activities. OPV 2 has been linked with many vaccine-derived outbreaks. In addition, 1 dose of injectable trivalent inactivated poliovirus vaccine (IPV) has been introduced into childhood immunization schedules to reduce risk of cVDPV2 outbreaks.
Initial efforts to introduce IPV were met with production challenges, and 20 countries have had to delay their introduction of IPV until adequate supplies are made available, according to the report.
As of August 31, 89% of the 194 World Health Organization countries have introduced IPV into their immunization schedules. In response to shortages, the Global Polio Eradication Initiative (GPEI) has prioritized allocation of IPV to Afghanistan, Pakistan, and Nigeria due to ongoing indigenous WPV transmission.
“The 721 cases of polio caused by cVDPV2s during 2006-2016 highlight both why the switch was necessary and why multiple precautions were taken to prevent cVDPV2s from emerging or spreading after the switch,” Lee M. Hampton, MD, of the CDC’s Global Immunization Division wrote in the report.
As of August 2016, no new cVDPV outbreaks have been identified.
Hampton LM, Farrell M, Ramirez-Gonzalez A, et al. Cessation of trivalent oral poliovirus vaccine and introduction of inactivated poliovirus vaccine – worldwide, 2016. MMWR Morbid Mortal Wkly Rep. 2016;65:934-938; doi: 10.15585/mmwr.mm6535a3