Introduction of Inactivated Poliovirus Vaccine and Switch from Trivalent to Bivalent Oral Poliovirus Vaccine - Worldwide, 2013-2016.

Since the 1988 World Health Assembly resolution to eradicate poliomyelitis (polio), transmission of wild poliovirus (WPV) has been interrupted in all countries except Afghanistan, Nigeria, and Pakistan. No polio cases caused by WPV type 2 (WPV2) have been identified since 1999, and WPV type 3 has not been detected since November 11, 2012. This progress has been achieved through widespread use of oral poliovirus vaccine (OPV), most commonly trivalent OPV (tOPV), which contains types 1, 2, and 3 live, attenuated polioviruses. OPV polioviruses can undergo genetic changes during intestinal replication, and rarely, in communities with low vaccination coverage, such changes can result in vaccine-derived polioviruses (VDPVs) capable of causing paralytic polio. Eliminating the risk for polio caused by VDPVs will require stopping all OPV use. Among 686 cases of paralytic polio caused by circulating VDPVs (cVDPVs) that have been detected since 2006, type 2 cVDPVs (cVDPV2s) accounted for >97%. To eliminate the risks posed by cVDPV2s, OPV serotype 2 will be withdrawn from all immunization activities and programs through a global, synchronized replacement of all tOPV with bivalent OPV (bOPV) containing only types 1 and 3 polioviruses. This switch from tOPV to bOPV is scheduled for April 2016. To reduce the risk for cVDPV2 outbreaks and to facilitate responses to outbreaks that do occur, injectable trivalent inactivated poliovirus vaccine (IPV) is being introduced into routine immunization schedules in all countries. As of June 24, 2015, 90 (46%) of 194 World Health Organization (WHO) member states were using IPV, 102 (53%) had established dates for the introduction of IPV, and two (1%) intended to introduce IPV in 2015 but had not set dates for doing so. In addition to IPV introduction in all countries, careful synchronization of the switch from tOPV to bOPV will be needed within and across all 156 countries currently using tOPV. This report summarizes progress in introducing IPV and preparations for the switch from tOPV to bOPV.