Experience With Inactivated Polio Vaccine Introduction and the "Switch" From Trivalent to Bivalent Oral Polio Vaccine in the World Health Organization's Western Pacific Region

The World Health Organization (WHO) Western Pacific Region (WPR) has maintained its polio-free status since 2000. The emergence of vaccine-derived polioviruses (VDPVs), however, remains a risk, as oral polio vaccine (OPV) is still used in many of the region's countries, and pockets of unimmunized or underimmunized children exist in some countries. From 2014 to 2016, the region participated in the globally coordinated efforts to introduce inactivated polio vaccine (IPV) into all countries that did not yet include it in their national immunization schedules, and to "switch" from trivalent OPV (tOPV) to bivalent OPV (bOPV) in all countries still using OPV in 2016. As of September 2016, 15 of 17 countries and areas that did not use IPV by the end of 2014 had introduced IPV. Introduction in the remaining 2 countries has been delayed because of the global shortage of IPV, making it unavailable to select lower-risk countries until the fourth quarter of 2017. All 16 countries using OPV as of 2016 successfully withdrew tOPV during the globally synchronized switch from April to May 2016, and 15 of 16 countries introduced bOPV at the same time, with the remaining country introducing it within 30 days. While countries were primarily responsible for self-funding these activities, additional support was provided. The main challenges encountered in the Western Pacific Region with both IPV introduction and the tOPV-bOPV switch were related to overcoming regulatory policies and challenges with vaccine procurement. As a result, substantial lead time was needed to resolve procurement and regulatory issues before the introductions of IPV and bOPV. As the global community prepares for the full removal of all OPV from immunization programs, this need for lead time and consideration of the impact on national policies should be considered.