Seroprevalence of poliovirus antibodies in Nigeria: refining strategies to sustain the eradication effort.

Introduction: in 2016, a switch from trivalent oral poliovirus vaccine (OPV) (containing serotypes 1,2,3) to bivalent OPV (types 1,3) was implemented globally. We assessed the seroprevalence of poliovirus antibody levels in selected Nigerian states, before and after the switch, documented poliovirus type2 outbreak responses conducted and ascertained factors associated with immunity gaps based on seroprevalence rates. Methods: we conducted a secondary analysis of stored serum samples from the 2018 Nigeria National HIV/AIDS Indicator and Impact Survey. Serum from 1,185 children aged 0-119 months residing in one southern and four northern states were tested for serotype-specific PV neutralizing antibodies; seropositivity was a reciprocal titer ≥8. We conducted regression analysis to determine sociodemographic risk factors associated with low seroprevalence using SAS 9.4. Results: children aged 24-119 months (pre-switch cohort) had seroprevalence against PV1, PV2, and PV3, of 97.3% (95% CI:96.4-98.2), 93.8% (95% CI:92.2-95.5), and 91.3% (95% CI:89.2-93.4), while children aged <24 months (post-switch) had seroprevalence of 86.0% (95% CI:81.2-90.8), 55.6% (95% CI: 47.7-63.4), and 77.2% (95% CI:71.0-83.4) respectively. Regression analysis showed age <24 months was associated with lower seroprevalence against all PV serotypes, (p<0.0001); females had lower seroprevalence against PV1 (p=0.0184) and PV2 (p=0.0354); northern states lower seroprevalence against PV1 (p=0.0039), while well-water source lower seroprevalence against PV3 (p=0.0288). Conclusion: this study showed high seroprevalence rates against PV 1, 2, and 3 in pre-switch children (aged 24-119 months). However, post-switch children (<24 months) had low immunity against PV2 despite outbreak responses. Strategies to increase routine immunization coverage and high-quality polio campaigns can increase immunity against polio virus.

An assessment of the contribution of National Stop Transmission of Polio Program to Nigeria's Immunization Program.

Introduction: In July 2012, the National Stop Transmission of Polio (NSTOP) program was established to support the Government of Nigeria in interrupting transmission of poliovirus and strengthen routine immunization (RI). NSTOP has approximately 300 staff members with the majority based at the Local Government Area (LGA) level in northern Nigeria. Methods: An internal assessment of NSTOP was conducted from November 2015 to February 2016 to document the program´s contribution to Nigeria´s immunization program and plan future NSTOP engagement. A mixed methods design was used, with data gathered from health facility, LGA, state, and national levels, through structured surveys, interviews, focus group discussions, and review of program records. Survey and expenditure data were summarized by frequency and trends over time, while interview and focus group data were analyzed qualitatively for key themes. Results: The majority of the 111 non-NSTOP LGA respondents reported that NSTOP officers supported polio campaigns (100%) and supervised RI sessions (99.1%). Out of 181 respondents at health facility level, the majority reported that NSTOP trainings improved their knowledge (83.3%) and skills (76.2%) on RI, and NSTOP officers regularly supervised their RI sessions (96.7%). Most respondents reported that there would be a negative impact on immunization activities if NSTOP officers were withdrawn. Conclusion: Future implementation of NSTOP should be realigned to (a) give highest priority to mentoring LGA staff to build institutional capacity, (b) ensure increased capacity translates to improved provision of RI services, and (c) improve routine review of program monitoring data to assess progress in both polio and RI programs.

Revelation of an important weakness in polio elimination efforts in Nigeria: a descriptive cross-sectional study of nomadic dynamics in Sokoto and Taraba States, May 2013.

Introduction: Operational gaps in the Global Polio Eradication Initiative implementation had been partly responsible for inadequate population immunity and the continued transmission of wild poliovirus in Nigeria before the African Region was declared polio-free in 2020. Missed opportunities to provide services in nomadic populations due to frequent mobility, lack of inclusion in microplans and the remoteness of their settlements were the major challenges. During May 2013 we conducted immunization outreach to nomadic and other underserved communities in Rabah LGA, Sokoto state, and Ardo Kola LGA, Taraba state, in Nigeria to identify and vaccinate children missed during supplemental immunization activities while identifying missed acute flaccid paralysis cases. Methods: An enumeration checklist and data collection instruments on Android cell phones were used to capture socio-demographic data and GPS coordinates on nomadic settlements, households, number of children aged <5 years, children previously missed for vaccination and their locations. Local guides led trained enumerators to underserved communities for the enumeration and vaccination. Data were analyzed using Microsoft Excel 2007. Results: A total of 324 settlements were listed for the two states, and 111 (34.3%) of these were identified as missed when compared with micro-planning for the most recent SIA. In these settlements, 3,533 households and 9,385 children aged <5 years were listed. We administered oral poliovirus vaccine to all 1,946 missed children during the recent or any supplemental immunization activities. Of these, 527 (27.1%) had never been vaccinated. We found no missed acute flaccid paralysis cases. Conclusion: Nomadic populations continue to be underserved, especially for vaccination services. This results in pockets of populations with low herd immunity and increased risk for poliovirus transmission. Community leaders and nomadic settlements should be included in the micro-planning of all supplemental immunization activities to ensure all children receive vaccination services.

Enhancing acute flaccid paralysis surveillance system towards polio eradication: reverse cold chain monitoring in Nigeria, 2017 to 2019.

Introduction: Highly sensitive acute flaccid paralysis (AFP) surveillance is critical for detection of poliovirus circulation and documentation for polio-free certification. The reverse cold chain (RCC) is a system designed to maintain stool specimens in appropriate temperature for effective detection of poliovirus in the laboratory. We monitored the RCC of AFP surveillance in Nigeria to determine its effectiveness in maintaining viability of enterovirus. Methods: A descriptive cross-sectional study was conducted from November 2017 to December 2019. We included AFP cases from 151 Local Government Areas and monitored RCC of paired stool specimens from collection to arrival at laboratories. The national guideline recommends RCC temperature of +2 to +8°C and a non-polio enterovirus (NPENT) detection rate of ≥10%. We analyzed data with Epi Info 7, and presented results as frequencies and proportions, using Chi-square statistic to test for difference in enterovirus isolation. Results: Of the 1,042 tracked paired stool specimens, 1,038(99.6%) arrived at the laboratory within 72 hours of collection of second specimen, 824(79.1%) were maintained within recommended temperature range, and 271(26%) yielded enteroviruses: 200(73.8%) NPENT, 66(24.4%) Sabin, 3(1.1%) vaccine derived poliovirus type 2 and 2(0.7%) mixture of Sabin and NPENT. The NPENT and Sabin rates were 19.2% and 6.7% respectively. Twenty-five percent of 824 specimens maintained within recommended temperature range, compared with 29.8% of 218 specimens with temperature excursion yielded enteroviruses (P=0.175). Conclusion: the RCC of AFP surveillance system in the study area was optimal and effective in maintaining the viability of enteroviruses. It was unlikely that poliovirus transmission was missed during the intervention.