Role of Serial Polio Seroprevalence Studies in Guiding Implementation of the Polio Eradication Initiative in Kano, Nigeria: 2011–2014

In 1988, the World Health Assembly resolved to eradicate poliomyelitis by 2000 [1]. Subsequently, the Global Polio Eradication Initiative (GPEI) was able to reduce the number of polio-endemic countries and wild poliovirus (WPV) cases from 125 and 350 000, respectively, in 1988 to 3 and 416, respectively, by 2013 [2]. Indigenous transmission of WPV types 2 and 3 (WPV2 and WPV3) has since been interrupted globally [3, 4]. Nigeria was one of 3 remaining polio-endemic countries in the world, alongside Afghanistan and Pakistan [5], but on 25 September 2015, following the historical interruption of transmission of WPV for 14 months, the World Health Organization (WHO) director general, Dr Margaret Chan, on behalf of the WHO, delisted Nigeria as a polio-endemic country after 17 years of the country's polio eradication effort. However, until 2012, Nigeria was the only country with transmission of all 3 poliovirus serotypes: WPV1, WPV3, and circulating vaccine-derived poliovirus type 2 (cVDPV2) [6], despite the conduct of multiple supplementary immunization activities (SIAs) and the use of more-immunogenic polio vaccines [7]. This indicated a substantial immunity gap, which led the country to determine how well children were protected against polio and where the remaining gaps driving persistent transmission were. Based on the recommendations in the GPEI 2010–2012 strategic plan [8] on the conduct of polio seroprevalence surveys (SPS), the Nigerian government, with GPEI partners, decided to implement polio SPS in the high-risk states of the country. The objective was to estimate the level of population immunity, measure the programmatic progress through repeat surveys, and provide valuable insight for development of innovative strategies to interrupt poliovirus transmission. Kano State has long been considered the epicenter of polio transmission in Nigeria and as one of the world's poliovirus sanctuaries [9, 10]. The state continues to be at high risk, such that even with substantial reduction in the recorded number of polio cases in Nigeria in 2014, it accounted for 5 of 6 WPV1 cases and 10 of 30 cVDPV2 cases in the country. By the recent joint WHO, Centers for Disease Control and Prevention (CDC), and Global Goods classification, 20 of the 38 local government areas (LGAs; 53%) at very high-risk (VHR) for polio transmission are from Kano State. All 8 urban LGAs of Kano Metropolitan Area (KMA)—Kano Municipal, Fagge, Nassarawa, Dala, Gwale, Tarauni, Ungogo, and Kumbotso—fall into this category. Based on this, Kano State, particularly the KMA (Figure ​(Figure1),1), was the natural first choice for the survey. Figure 1. A map of the study area, Kano Metropolitan Area, in Kano State, northern Nigeria. Abbreviation: LGA, local government area. Previous work has been done to measure and report the seroprevalence of polio serotypes among different age groups. Giwa et al reported that seroprevalence to poliovirus serotypes, although higher than values found in previous studies done in Nigeria, was lower than in the developed world [11]. This was corroborated by Iliyasu et al, who submitted that seroprevalence levels found in their survey, specific to Kano, were much lower than in corresponding serosurveys in Egypt and India [12, 13] and are insufficient to interrupt poliovirus transmission [14]. We present results of serial health facility–based polio seroprevalence surveys conducted in the 8 urban LGAs of KMA in Kano State, focusing on infants aged 6–9 months and comparing their seroprevalence levels in 2011, 2013, and 2014 to show how findings of these SPS have been used to review the polio eradication program in Nigeria and to subsequently develop innovative strategies for polio eradication.