Discussion

Substantial gains toward polio eradication were made in 2015, with a 79% decrease in the number of polio cases reported worldwide compared with the number of cases reported in 2014. The removal of Nigeria from the list of countries with endemic polio in 2015 creates the opportunity for the African Region to join the Region of the Americas and the South-East Asia, Western Pacific, and European regions, as the fifth of six WHO regions to be certified free of indigenous WPV. Certification will occur after a minimum of 3 years of sensitive AFP surveillance. In addition, the Global Commission for the Certification of Poliomyelitis Eradication’s declaration of the eradication of WPV type 2 in 2015, and the absence of reported circulation of WPV type 3 since 2012, allows focus on WPV type 1 as the sole circulating type of WPV in the world, endemic only in Afghanistan and Pakistan. WHO considers the continued transmission of WPV type 1 between both countries to constitute a public health emergency of international concern under the 2005 International Health Regulations.¶ Continued focus on identifying groups of children who missed polio vaccination through routine immunization or SIAs, improving SIA quality, and increasing AFP surveillance sensitivity in these countries is needed to stop transmission.

In 2015, Afghanistan had a major reduction in WPV cases. The majority of cases were reported from Nangarhar province in eastern Afghanistan, which borders Pakistan, and were genetically linked to cases in Pakistan, emphasizing the need for continued improvement of cross-border coordination and SIA synchronization. Although some children are missed during SIAs in Afghanistan because of inaccessibility and security concerns, the majority are missed during SIAs because of managerial issues, including inadequate microplanning and campaign implementation. The southern region, although accessible for program implementation, has very limited access for supervision and monitoring. Innovative approaches, such as the 4th-day revisit strategy during campaigns, the use of permanent vaccination teams dedicated to regular house-to-house visits, and vaccination at transit points leading in and out of insecure areas need to continue to be regularly used to reach all missed children (5). The recent establishment of emergency operations centers at the national level and in three critical regions enhances the country’s capacity to plan and implement polio eradication activities.

Progress in Pakistan accounted for most of the sharp decline in the number of polio cases during 2015–2016. The substantial gains made are, at least in part, attributable to the establishment of a cohesive national emergency operations center that implemented a rigorous National Polio Eradication Emergency Action Plan (6). However, operational problems with vaccination of all children during SIAs, program accountability at all levels, and ongoing movement of unvaccinated children across the Afghanistan-Pakistan border remain challenges facing the polio program in Pakistan.

Although no WPV cases were detected in countries without endemic WPV circulation, seven countries reported cVDPV outbreaks during 2015–2016, demonstrating the risk for VDPV emergence associated with low OPV coverage. In each of these countries, certain factors, such as the concurrent Ebola epidemic in Guinea and instability in vaccine procurement and public trust in Ukraine, diminished the quality of routine immunization services and allowed the emergence and spread of the outbreaks. Approximately 95% of cVDPV cases since 2006 have been caused by cVDPV2 (9). Therefore, with certification of the eradication of WPV type 2, in April 2016, 154 of 155 planned countries and territories** discontinued use of type 2 Sabin vaccine by switching from tOPV to bOPV for routine and supplementary immunization during a globally synchronized initiative that spanned 2 weeks, from April 17–May 1, 2016 (9). The global switch from tOPV to bOPV will markedly reduce the risk associated with type 2 cVDPV emergence and transmission; however, the global community must continue to support strong routine immunization service delivery to curb the risk for type 1 or type 3 cVDPV outbreaks or transmission after WPV importation from countries with endemic poliovirus transmission.

With progress made during 2015–2016 toward interruption of WPV transmission in Afghanistan and Pakistan, the world is closer than ever to the eradication of polio. Continued cooperation between the two countries is needed for this goal to be reached. In addition, the greater worldwide community needs to remain vigilant in implementing the Global Polio Eradication Initiative’s Polio Eradication and Endgame Strategic Plan for 2013–2018 to end WPV and VDPV transmission (10).