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Background: Between 2018 and 2022, Nigeria experienced continuous transmission of circulating vaccine-derived type 2 poliovirus (cVDPV2), with 526 cases of cVDPV2 poliomyelitis detected in total and approximately 180 million doses of monovalent type 2 oral poliovirus vaccine (mOPV2) and 450 million doses of novel type 2 oral poliovirus vaccine (nOPV2) delivered in outbreak response campaigns. Inactivated poliovirus vaccine (IPV) was introduced into routine immunisation in 2015, with a second dose added in 2021. We aimed to estimate the effectiveness of nOPV2 against cVDPV2 paralysis and compare nOPV2 effectiveness with that of mOPV2 and IPV., Methods: In this retrospective case-control study, we used acute flaccid paralysis (AFP) surveillance data in Nigeria from Jan 1, 2017, to Dec 31, 2022, using age-matched, onset-matched, and location-matched cVDPV2-negative AFP cases as test-negative controls. We also did a parallel prospective study from March, 2021, using age-matched community controls from the same settlement as the cases. We included children born after May, 2016, younger than 60 months, for whom polio immunisation history (doses of OPV from campaigns and IPV) was reported. We estimated the per-dose effectiveness of nOPV2 against cVDPV2 paralysis using conditional logistic regression and compared nOPV2 effectiveness with that of mOPV2 and IPV., Findings: In the retrospective case-control study, we identified 509 cVDPV2 poliomyelitis cases in Nigeria with case verification and paralysis onset between Jan 1, 2017, and Dec 31, 2022. Of these, 82 children were excluded for not meeting inclusion criteria, and 363 (85%) of 427 eligible cases were matched to 1303 test-negative controls. Cases reported fewer OPV and IPV doses than test-negative controls (mean number of OPV doses 5·9 [SD 4·2] in cases vs 6·7 [4·3] in controls; one or more IPV doses reported in 95 [26%] of 363 cases vs 513 [39%] of 1303 controls). We found low per-dose effectiveness of nOPV2 (12%, 95% CI -2 to 25) and mOPV2 (17%, 3 to 29), but no significant difference between the two vaccines (p=0·67). The estimated effectiveness of one IPV dose was 43% (23 to 58). In the prospective study, 181 (46%) of 392 eligible cases were matched to 1557 community controls. Using community controls, we found a high effectiveness of IPV (89%, 95% CI 83 to 93, for one dose), a low per-dose effectiveness of nOPV2 (-23%, -45 to -5) and mOPV2 (1%, -23 to 20), and no significant difference between the per-dose effectiveness of nOPV2 and mOPV2 (p=0·12)., Interpretation: We found no significant difference in estimated effectiveness of the two oral vaccines, supporting the recommendation that the more genetically stable nOPV2 should be preferred in cVDPV2 outbreak response. Our findings highlight the role of IPV and the necessity of strengthening routine immunisation, the primary route through which IPV is delivered., Funding: Bill & Melinda Gates Foundation and UK Medical Research Council., Competing Interests: Declaration of interests We declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license. Published by Elsevier Ltd.. All rights reserved.)

Background: Novel oral poliovirus vaccine (OPV) type 2 (nOPV2) has been made available for outbreak response under an emergency use listing authorization based on supportive clinical trial data. Since 2021 more than 350 million doses of nOPV2 were used for control of a large outbreak of circulating vaccine-derived poliovirus type 2 (cVDPV2) in Nigeria., Methods: Using a bayesian time-series susceptible-infectious-recovered model, we evaluate the field effectiveness of nOPV2 immunization campaigns in Nigeria compared with campaigns using monovalent OPV type 2 (mOPV2)., Results: We found that both nOPV2 and mOPV2 campaigns were highly effective in reducing transmission of cVDPV2, on average reducing the susceptible population by 42% (95% confidence interval, 28-54%) and 38% (20-51%) per campaign, respectively, which were indistinguishable from each other in this analysis (relative effect, 1.1 [.7-1.9]). Impact was found to vary across areas and between immunization campaigns., Conclusions: These results are consistent with the comparable individual immunogenicity of nOPV2 and mOPV2 found in clinical trials but also suggest that outbreak response campaigns may have small impacts in some areas requiring more campaigns than are suggested in current outbreak response procedures., Competing Interests: Potential conflicts of interest. A. V., H. L., A. S. B., and S. O. are employed by the Bill & Melinda Gates Foundation. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)

Introduction: following the spread of the COVID-19 pandemic to Nigeria, the Federal Government of Nigeria restricted human and vehicular movements to curb the spread of the disease. This action had a negative impact on Acute Flaccid Paralysis (AFP) surveillance, with a resultant reduction in the number of AFP cases reported. This paper describes the impact of the COVID-19 pandemic on poliovirus surveillance in Nigeria and the proactive interventions by Nigeria´s polio program to mitigate the impact of COVID-19 on polio surveillance., Methods: nine innovative strategies were implemented in all 774 Local Government Areas (LGA) of the 36 states and Federal Capital Territory (FCT) of the country. These strategies were developed by the national surveillance officers and operationalized by sub-national surveillance officers with different strategies starting at different epidemiological weeks from week 14 to 23, 2020. Many of the strategy innovations were technology-based and included: the use of mobile phones to send the AFP case definition and video by WhatsApp or by SMS, the use of state-specific toll-free numbers and Mobile Telephone Network (MTN) (mobile service provider) CallerfeelTM to community informants (CI) who were the main targets of the interventions to increase case detection and reporting. Others included the use of abridged e-surveillance integrated supportive supervision (ISS) checklists, virtual monthly DSNO meetings, and batched AFP stool specimen transportation network., Results: compared to the same period in 2019, the cumulative rate of AFP case detection and reporting had gradually declined from 39.1% in January to 16.7% before the commencement of the interventions in week 20, 2020. However, the detection and reporting increased by 57.% from week 20 to week 47 compared to the same period in 2019. This is because with COVID-19, hospital visitation dropped, and the sick remained in the communities, so the CI network was relied on to detect and report AFP cases. The cumulative proportion of AFP cases reported by community informants as of week 47 increased from 13% in 2018 to 21% in 2020. This indicates an increase of 38%. Thirty-five AFP cases were detected and reported using the MTN Caller Feel strategy, while 15 cases were reported through state-specific toll-free numbers., Conclusion: the implementation of the innovative strategies was able to mitigate the low AFP case detection and reporting observed at the initial stage of the COVID-19 pandemic. The use of technology facilitated reaching the CI network, which was more instrumental in detecting and reporting the cases., Competing Interests: The authors declare no competing interests., (©Aboyowa Arayuwa Edukugho et al.)

Introduction: acute flaccid paralysis (AFP) surveillance is the gold standard of the Global Polio Eradication Initiative (GPEI) for detecting cases of poliomyelitis and tracking poliovirus transmission. Nigeria's AFP surveillance performance indicators are among the highest in countries of the World Health Organization (WHO) African Region. The primary AFP surveillance performance indicators are the rate of non-polio AFP among children and the proportion of timely, adequate specimen collection. The surveillance working group of the National Emergency Operations Centre assessed the quality of AFP surveillance data in some reportedly high-performing states., Methods: we conducted a retrospective review of AFP surveillance performance indicators in Nigeria for 2010-2019. We also reviewed data in reports from four groups of surveillance peer reviews and validation visits (conducted by in-country GPEI partners) during August 2017-May 2019 in 16 states with high primary AFP surveillance indicators; the validation visits reviewed clinical information and the dates of specimen collection and onset of paralysis with caretakers., Results: there were consistently increasing AFP surveillance primary performance indicators during 2010-2016, followed by declines during 2017-2019. From the data for 16 states with peer reviews conducted from August 2017-May 2019, overall concordance of reported and "true" (validated) AFP indicator data in peer review investigations was highly variable. True AFP concordance ranged from 58%-100%, and stool timeliness concordance ranged from 56%-95%. The most common clinical causes of reported AFP cases that were not true AFP were spastic paralysis, malaria, sickle cell disease, and malnutrition. All the states that participated in peer reviews developed surveillance improvement plans based on the gaps identified., Conclusion: Nigeria has highly sensitive AFP surveillance according to reported primary AFP performance indicators. The findings of peer reviews indicate that the AFP surveillance system needs to be strengthened and well-supervised to enhance data quality., Competing Interests: The authors declare no competing interests., (©Abdullahi Walla Hamisu et al.)

Introduction: ultimately detected in 2016, wild poliovirus (WPV) transmission continued undetected after 2011 in Northeast Nigeria Borno and Yobe States in security-compromised areas, inaccessible due to armed insurgency. Varying inaccessibility prevented children aged <5 years in these areas from polio vaccination interventions and surveillance, while massive population displacements occurred. We examined progress in access over time to provide data supporting a very low probability of undetected WPV circulation within remaining trapped populations after 2016., Methods: to assess the extent of inaccessibility in security-compromised areas, we obtained empirical historical data in 2020 on a quarterly and annual basis from relevant polio eradication staff for the period 2010-2020. The extent of access to areas for immunization by recall was compared to geospatial data from vaccinator tracking. Population estimates over time in security-compromised areas were extracted from satellite imagery. We compared the historical access data from staff with tracking and population esimates., Results: access varied during 2010-2020, with inaccessibility peaking during 2014-2016. We observed concurrent patterns between historical recalled data on inaccessibility and contemporaneous satellite imagery on population displacements, which increased confidence in the quality of recalled data., Conclusion: staff-recalled access was consistent with vaccinator tracking and satellite imagery of population displacments. Despite variability in inaccessibility over time, innovative immunization initiatives were implemented as access allowed and surveillance initiatives were initiated to search for poliovirus transmission. Along with escape and liberation of residents by the military in some geographic areas, these initiatives resulted in a massive reduction in the size of the unvaccinated population remaining resident., Competing Interests: The authors declare no competing interests., (©Joseph Che Forbi et al.)

Introduction: novel oral poliovirus vaccine type 2 (nOPV2), designed to be more genetically stable than Sabin-strain oral poliovirus vaccine type 2 (mOPV2), is a new and key component of the Global Polio Eradication Initiative's strategy to combat outbreaks of circulating vaccine-derived poliovirus type 2 (cVDPV2). The World Health Organization´s (WHO´s) emergency use listing (EUL) requires extensive safety monitoring for Adverse Event of Special Interest (AESI) in its use. We implemented AESI active surveillance to monitor the safety of the nOPV2 in Nigeria., Methods: a cross-sectional assessment was conducted in Nigeria during March-June 2021 in 117 local government areas (LGAs) across 6 states and the Federal Capital Area with confirmed cVDPV2 transmission. We conducted active searches for nOPV2 AESI in all health facilities. Suspected events were ascertained, and vaccination and clinical data abstracted. Events were classified using WHO causality assessment algorithm. Data were analyzed using Epi info7., Results: total of 234 adverse events were reported after 21,997,300 doses of nOPV2 were administered, giving a crude reported incidence of 1 in 94,000 doses of nOPV2. Altogether, 221 of the 234 (94%) adverse events were classified. For 166 AESI ascertained to occur following a dose of nOPV2, the corrected crude incidence rate was 1 in 133,000 doses; 4 of the adverse events, were classified as consistent with casual association with nOPV2 vaccination., Conclusion: we found that nOPV2 had a low incidence of AESI following nOPV2 campaigns and no new or unexpected adverse event was reported. Safety monitoring should be sustained for early detection of signals and uncommon adverse events., Competing Interests: The authors declare no competing interests., (©Samuel Luka Abbott et al.)

Introduction: in August 2020, the World Health Organization African Region was certified free of wild poliovirus (WPV) when Nigeria became the last African country to interrupt wild poliovirus transmission. The National Polio Emergency Operations Center instituted in 2012 to coordinate and manage Nigerian polio eradication efforts reviewed the epidemiology of WPV cases during 2000-2020 to document lessons learned., Methods: we analyzed reported WPV cases by serotype based on age, oral poliovirus vaccine immunization history, month and year of reported cases, and annual geographic distribution based on incidence rates at the Local Government Area level. The observed trends of cases were related to major events and the poliovirus vaccines used during mass vaccination campaigns within the analysis period., Results: a total of 3,579 WPV type 1 and 1,548 WPV type 3 laboratory-confirmed cases were reported with onset during 2000-2020. The highest WPV incidence rates per 100,000 population in Local Government Areas were 19.4, 12.0, and 11.3, all in 2006. Wild poliovirus cases were reported each year during 2000-2014; the endemic transmission went undetected throughout 2015 until the last cases in 2016. Ten events/milestones were highlighted, including insurgency in the northeast which led to a setback in 2016 with four cases from children previously trapped in security-compromised areas., Conclusion: Nigeria interrupted WPV transmission despite the challenges faced because of the emergency management approach, implementation of mass vaccination campaigns, the commitment of the government agencies, support from global polio partners, and special strategies deployed to conduct vaccination and surveillance in the security-compromised areas., Competing Interests: The authors declare no competing interests., (©Philip Bammeke et al.)

Introduction: in Nigeria, supportive supervision of Supplementary Immunization Activities (SIA) is a quality improvement strategy for providing support to vaccination teams administering the poliovirus vaccines to children under 5 years of age. Supervision activities were initially reported in paper forms. This had significant limitations, which led to Open Data Kit (ODK) technology being adopted in March 2017. A review was conducted to assess the impact of ODK for supervision reporting in place of paper forms., Methods: issues with paper-based reporting and the benefits of ODK were recounted. We determined the average utilization of ODK per polio SIA rounds and assessed the supervision coverage over time based on the proportion of local government areas with ODK geolocation data per round., Results: a total of 17 problematic issues were identified with paper-based reporting, and ODK addressed all the issues. Open Data Kit-based supervision reports increased from 3,125 in March 2017 to 51,060 in February 2020. Average ODK submissions for national rounds increased from 84 in March 2017 to 459 in February 2020 and for sub-national rounds increased from 533 in July 2017 to 1,596 in October 2019. Supportive supervision coverage improved from 42.5% in March 2017 to 97% in February 2020., Conclusion: the use of digital technologies in public health has comparative advantages over paper forms, and the adoption of ODK for supervision reporting during polio SIAs in Nigeria experienced the advantages. The visibility and coverage of supportive supervision improved, consequentially contributing to the improved quality of polio SIAs., Competing Interests: The authors declare no competing interests., (©Philip Bammeke et al.)

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., (©Samuel Luka Abbott et al.)