Circulating vaccine-derived polioviruses (cVDPVs) can emerge and lead to outbreaks of paralytic polio as well as asymptomatic transmission in communities with a high percentage of undervaccinated children. Using data from the World Health Organization Polio Information System and Global Polio Laboratory Network, this report describes global polio outbreaks due to cVDPVs during January 2023-June 2024 and updates previous reports. During the reporting period, 74 cVDPV outbreaks were detected in 39 countries or areas (countries), predominantly in Africa. Among these 74 cVDPV outbreaks, 47 (64%) were new outbreaks, detected in 30 (77%) of the 39 countries. Three countries reported cVDPV type 1 (cVDPV1) outbreaks and 38 countries reported cVDPV type 2 (cVDPV2) outbreaks; two of these countries reported cocirculating cVDPV1 and cVDPV2. In the 38 countries with cVDPV2 transmission, 70 distinct outbreaks were reported. In 15 countries, cVDPV transmission has lasted >1 year into 2024. In Nigeria and Somalia, both countries with security-compromised areas, persistent cVDPV2 transmission has spread to neighboring countries. Delayed implementation of outbreak response campaigns and low-quality campaigns have resulted in further international spread. Countries can control cVDPV outbreaks with timely allocation of resources to implement prompt, high-quality responses after outbreak confirmation. Stopping all cVDPV transmission requires effectively increasing population immunity by overcoming barriers to reaching children.

In 2022, global poliovirus modeling suggested that coordinated cessation of bivalent oral poliovirus vaccine (bOPV, containing Sabin-strain types 1 and 3) in 2027 would likely increase the risks of outbreaks and expected paralytic cases caused by circulating vaccine-derived polioviruses (cVDPVs), particularly type 1. The analysis did not include the implementation of planned, preventive supplemental immunization activities (pSIAs) with bOPV to achieve and maintain higher population immunity for types 1 and 3 prior to bOPV cessation. We reviewed prior published OPV cessation modeling studies to support bOPV cessation planning. We applied an integrated global poliovirus transmission and OPV evolution model after updating assumptions to reflect the epidemiology, immunization, and polio eradication plans through the end of 2023. We explored the effects of bOPV cessation in 2027 with and without additional bOPV pSIAs prior to 2027. Increasing population immunity for types 1 and 3 with bOPV pSIAs (i.e., intensification) could substantially reduce the expected global risks of experiencing cVDPV outbreaks and the number of expected polio cases both before and after bOPV cessation. We identified the need for substantial increases in overall bOPV coverage prior to bOPV cessation to achieve a high probability of successful bOPV cessation.

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.

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.

INTRODUCTION: to support polio eradication activities in Nigeria, in 2012 the National Polio Emergency Operation Center (NEOC) created the Management Support Teams (MST) to address gaps in the quality of supervision of polio vaccination teams. The National Stop Transmission of Polio (NSTOP) Program supported the polio eradication activities by deploying trained supervisors as part of the MST for polio and non-polio immunization campaigns. METHODS: trained MST members were deployed approximately 4 days before the start of the campaign to participate in pre-implementation activities and supervise vaccination teams during campaigns. Terms of reference (TOR) developed by NEOC was provided to MST members to guide their activities. Qualified MSTs that met pre-determined criteria were selected and deployed to the field to support pre, intra and post campaigns activities. RESULTS: a pool of over 400 MST personnel have been identified, trained, and repeatedly deployed from 2012 till 2016. The number of deployed MST personnel rose from 40 per campaign in October 2012 to 342 in May 2016. Of these, 270 (79%) MST personnel were deployed to 11 polio high-risk states of northern Nigeria, where campaigns are conducted between eight and ten times yearly as planned by NEOC. For measles campaigns, about 300 (75%) MST personnel were deployed for the one-off northern and southern campaigns in 2016. The results of clustered Lot Quality Assurance Sampling (LQAS) post-campaign vaccination coverage surveys, a measure of campaign quality, of which introduction into the polio program coincided with deployment of MSTs, showed improvement over time, from 10% (very poor quality) in February 2012 to about 90% (good quality) in December 2016. CONCLUSION: the deployment of MST personnel increased the number of trained supervisors in the field, frequency of supervisory visits and had a positive impact on the quality of polio campaigns.

INTRODUCTION: Acute flaccid paralysis (AFP) pictorial surveillance reminder cards (AFP cards) could aid AFP case identification during supplementary immunization activities (SIAs). We assessed the availability and utilization of AFP cards among vaccination teams during the December 2014 polio SIAs in Jigawa State, Nigeria. METHODS: We conducted a cross-sectional survey of a convenience sample of 95 vaccination team supervisors. We used a semi-structured interviewer-administered questionnaire to collect information on socio-demographics, knowledge of AFP cases, availability and utilization of the AFP cards for case identification and investigation and non-compliance resolution by vaccination teams. Univariate and bivariate analyses were performed using Epi Info version 3.5.1. RESULTS: Of the 95 supervisors interviewed, 86 (91%) reported that vaccinators properly displayed the AFP cards, 90 (95%) reported use of cards for AFP case identification, 88 (93%) reported use of cards to resolve non-compliance with polio vaccination and 77 (81%) reported use of cards to ask caregivers six key questions to prevent missed children. Fifty-eight (61%) supervisors knew the AFP case definition. A total of 21 possible AFP cases were identified by vaccination team members with the aid of the cards, of which 17 (81%) were referred to the nearest health facility. CONCLUSION: The survey demonstrated usefulness of reminder cards for identification and follow-up of AFP cases. Based on these findings, use of AFP cards was implemented in all Nigerian States and similar cards were developed and implemented for measles surveillance during SIAs.

INTRODUCTION: The National Stop Transmission of Polio (NSTOP) program was created in 2012 to support the Polio Eradication Initiative (PEI) in Local Government Areas (LGAs) at high risk for polio in Northern Nigeria. We assessed immunization service delivery prior to the commencement of NSTOP support in 2014 and after one year of implementation in 2015 to measure changes in the implementation of key facility-based Routine Immunization (RI) components. METHODS: The pre- and post-assessment was conducted in selected health facilities (HFs) in 61 LGAs supported by NSTOP in 5 states. A standardized questionnaire was administered to the LGA and HF immunization staff by trained interviewers on key RI service delivery components. RESULTS: At the LGA level, an increase was observed in key components including availability of updated Reach Every Ward (REW) micro-plans with identification of hard to reach settlements (65.6% baseline, 96.8% follow-up, PR = 1.5 (95% CI 3.4 - 69.8), vaccine forecasting (77.1% baseline, 93.5% follow-up, PR =1.2 (95% CI 1.8 - 13.8), and timely delivery of monthly immunization reports (73.8% baseline, 90.2% follow-up; PR =1.2 (95% CI 1.2 - 9.0). At the HF level, there was an increase in percentage of HFs with written supervisory feedback (44.5% baseline, 82.5% follow-up, PR = 1.8 (95% CI 4.7 - 7.3), written stock records (66.5% baseline, 87.9% follow-up, PR = 1.3 (95% CI 2.9 - 4.7) and updated immunization monitoring charts (76.3% baseline, 95.6% follow-up, PR = 1.3 (95% CI 4.6 - 9.9). CONCLUSION: We observed an improvement in key RI service delivery components following implementation of NSTOP program activities in supported LGAs.

INTRODUCTION: Timely and accurate data are necessary for informing sound decision-making and developing effective routine immunization (RI) programs. We launched a pilot project in Kano State to strengthen routine immunization (RI) data reporting through the immunization module of the District Health Information System version 2 (DHIS2). We examined the completeness and timeliness of reporting monthly RI data one year before and one year after DHIS2 module pilot in the State. METHODS: The first phase of the DHIS2 RI module pilot in Kano included training on RI data tools in November 2014 and in January 2015 for 36 state and zonal personnels, 276 local government area (LGA) personnel, and 2,423 health facility (HF) staff. A RI-focused dashboard to display core RI accountability framework indicators, such as completeness and timeliness of reporting, planned immunization sessions conducted, coverage and dropout was implemented. Report completeness was ratio of submitted reports to number of health facilities while report timeliness was ratio of reports on the DHIS2 by 14th of the month to number of expected. RESULTS: Completeness of data reporting increase from 70% in 2014 to 87% in 2015, while timeliness of reporting increase from 64% to 87% over the same period. Challenges encountered during the implementation process included limited access to internet, power outages, health workers strike, staff attrition and competing state activities. CONCLUSION: The pilot implementation of the DHIS2 immunization module in Kano State led to modest improvement in the reporting of RI services. Several lessons learned were used to guide scale-up to other states in the country.

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.

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.

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.

After the 2015 documentation of global eradication of wild poliovirus type 2,* Sabin type 2 oral poliovirus vaccine (OPV) was withdrawn from routine immunization (RI) in all OPV-using countries in 2016, in a global synchronized switch from trivalent OPV (containing vaccine virus serotypes 1, 2, and 3) to bivalent OPV (containing serotypes 1 and 3), to reduce the rare risks for type 2 vaccine-associated paralytic poliomyelitis. Concurrently, the Global Polio Eradication Initiative (GPEI) recommended that all OPV-using countries introduce ≥1 dose of inactivated poliovirus vaccine (IPV) into RI programs; IPV protects against paralysis caused by all three serotypes but cannot be transmitted from person to person or cause paralysis. Use of OPV, especially in areas with low vaccination coverage, is associated with low risk of emergence of vaccine-derived polioviruses (VDPVs). As susceptible persons in new birth cohorts accumulated after withdrawal of OPV type 2, population immunity against infection with serotype 2 declined (1), facilitating the emergence of circulating VDPV type 2 (cVDPV2). During the previous 7 years, cVDPV2 outbreaks required response supplementary immunization activities (SIAs) with monovalent type 2 OPV (mOPV2); however, if SIAs were not of sufficiently high quality and did not achieve high enough coverage, new emergences of cVDPV2 occurred.

Background: The polio eradication endgame continues to increase in complexity.  With polio cases caused by wild poliovirus type 1 and circulating vaccine-derived polioviruses of all three types (1, 2 and 3) reported in 2022, the number, formulation, and use of poliovirus vaccines poses challenges for national immunization programs and vaccine suppliers.  Prior poliovirus transmission modeling of globally-coordinated type-specific cessation of oral poliovirus vaccine (OPV) assumed creation of Sabin monovalent OPV (mOPV) stockpiles for emergencies and explored the potential need to restart OPV if the world reached a specified cumulative threshold number of cases after OPV cessation. Methods:  We document the actual experience of type 2 OPV (OPV2) cessation and reconsider prior modeling assumptions related to OPV restart.  We develop updated decision trees of national immunization options for poliovirus vaccines considering different possibilities for OPV restart. Results:  While OPV restart represented a hypothetical situation for risk management and contingency planning to support the 2013-2018 Global Polio Eradication Initiative (GPEI) Strategic Plan, the actual epidemiological experience since OPV2 cessation raises questions about what, if any, trigger(s) could lead to restarting the use of OPV2 in routine immunization and/or plans for potential future restart of type 1 and 3 OPV after their respective cessation.  The emergency use listing of a genetically stabilized novel type 2 OPV (nOPV2) and continued evaluation of nOPV for types 1 and/or 3 add further complexity by increasing the combinations of possible OPV formulations for OPV restart.  Conclusions: Expanding on a 2019 discussion of the logistical challenges and implications of restarting OPV, we find a complex structure of the many options and many issues related to OPV restart decisions and policies as of early 2023.  We anticipate many challenges for forecasting prospective vaccine supply needs during the polio endgame due to increasing potential combinations of poliovirus vaccine choices.

Due to the very low, but nonzero, paralysis risks associated with the use of oral poliovirus vaccine (OPV), eradicating poliomyelitis requires ending all OPV use globally. The Global Polio Eradication Initiative (GPEI) coordinated cessation of Sabin type 2 OPV (OPV2 cessation) in 2016, except for emergency outbreak response. However, as of early 2023, plans for cessation of bivalent OPV (bOPV, containing types 1 and 3 OPV) remain undefined, and OPV2 use for outbreak response continues due to ongoing transmission of type 2 polioviruses and reported type 2 cases. Recent development and use of a genetically stabilized novel type 2 OPV (nOPV2) leads to additional potential vaccine options and increasing complexity in strategies for the polio endgame. Prior applications of integrated global risk, economic, and poliovirus transmission modeling consistent with GPEI strategic plans that preceded OPV2 cessation explored OPV cessation dynamics and the evaluation of options to support globally coordinated risk management efforts. The 2022-2026 GPEI strategic plan highlighted the need for early bOPV cessation planning. We review the published modeling and explore bOPV cessation immunization options as of 2022, assuming that the GPEI partners will not support restart of the use of any OPV type in routine immunization after a globally coordinated cessation of such use. We model the potential consequences of globally coordinating bOPV cessation in 2027, as anticipated in the 2022-2026 GPEI strategic plan. We do not find any options for bOPV cessation likely to succeed without a strategy of bOPV intensification to increase population immunity prior to cessation.

In May 2016, the Global Polio Eradication Initiative (GPEI) coordinated the cessation of all use of type 2 oral poliovirus vaccine (OPV2), except for emergency outbreak response. Since then, paralytic polio cases caused by type 2 vaccine-derived polioviruses now exceed 3,000 cases reported by 39 countries. In 2022 (as of April 25, 2023), 20 countries reported detection of cases and nine other countries reported environmental surveillance detection, but no reported cases. Recent development of a genetically modified novel type 2 OPV (nOPV2) may help curb the generation of neurovirulent vaccine-derived strains; its use since 2021 under Emergency Use Listing is limited to outbreak response activities. Prior modeling studies showed that the expected trajectory for global type 2 viruses does not appear headed toward eradication, even with the best possible properties of nOPV2 assuming current outbreak response performance. Continued persistence of type 2 poliovirus transmission exposes the world to the risks of potentially high-consequence events such as the importation of virus into high-transmission areas of India or Bangladesh. Building on prior polio endgame modeling and assuming current national and GPEI outbreak response performance, we show no probability of successfully eradicating type 2 polioviruses in the near term regardless of vaccine choice. We also demonstrate the possible worst-case scenarios could result in rapid expansion of paralytic cases and preclude the goal of permanently ending all cases of poliomyelitis in the foreseeable future. Avoiding such catastrophic scenarios will depend on the development of strategies that raise population immunity to type 2 polioviruses.

Since the Global Polio Eradication Initiative (GPEI) began in 1988, the number of wild poliovirus (WPV) cases has declined by >99.99%. Five of the six World Health Organization (WHO) regions have been certified free of indigenous WPV, and WPV serotypes 2 and 3 have been declared eradicated globally (1). WPV type 1 (WPV1) remains endemic only in Afghanistan and Pakistan (2,3). Before the outbreak described in this report, WPV1 had not been detected in southeastern Africa since the 1990s, and on August 25, 2020, the WHO African Region was certified free of indigenous WPV (4). On February 16, 2022, WPV1 infection was confirmed in one child living in Malawi, with onset of paralysis on November 19, 2021. Genomic sequence analysis of the isolated poliovirus indicated that it originated in Pakistan (5). Cases were subsequently identified in Mozambique. This report summarizes progress in the outbreak response since the initial report (5). During November 2021-December 2022, nine children and adolescents with paralytic polio caused by WPV1 were identified in southeastern Africa: one in Malawi and eight in Mozambique. Malawi, Mozambique, and three neighboring countries at high risk for WPV1 importation (Tanzania, Zambia, and Zimbabwe) responded by increasing surveillance and organizing up to six rounds of national and subnational polio supplementary immunization activities (SIAs).* Although no cases of paralytic WPV1 infection have been reported in Malawi since November 2021 or in Mozambique since August 2022, undetected transmission might be ongoing because of poliovirus surveillance gaps and testing delays. Efforts to further enhance poliovirus surveillance sensitivity, improve SIA quality, and strengthen routine immunization are needed to ensure that WPV1 transmission has been interrupted within 12 months of the first case, thereby preserving the WHO African Region's WPV-free status.

BACKGROUND: Trivalent oral poliovirus vaccine (tOPV) was globally replaced with bivalent oral poliovirus vaccine (bOPV) in April 2016 ("the switch"). Many outbreaks of paralytic poliomyelitis associated with type 2 circulating vaccine-derived poliovirus (cVDPV2) have been reported since this time. The Global Polio Eradication Initiative (GPEI) developed standard operating procedures (SOPs) to guide countries experiencing cVDPV2 outbreaks to implement timely and effective outbreak response (OBR). To assess the possible role of compliance with SOPs in successfully stopping cVDPV2 outbreaks, we analyzed data on critical timelines in the OBR process. METHODS: Data were collected on all cVDPV2 outbreaks detected for the period April 1, 2016 and December 31, 2020 and all outbreak responses to those outbreaks between April 1, 2016 and December 31, 2021. We conducted secondary data analysis using the GPEI Polio Information System database, records from the Anonymized Institution Poliovirus Laboratory, and meeting minutes of the monovalent OPV2 (mOPV2) Advisory Group. Date of notification of circulating virus was defined as Day 0 for this analysis. Extracted process variables were compared with indicators in the GPEI SOP version 3.1. RESULTS: One hundred and eleven cVDPV2 outbreaks resulting from 67 distinct cVDPV2 emergences were reported during April 1, 2016-December 31, 2020, affecting 34 countries across four World Health Organization Regions. Out of 65 OBRs with the first large-scale campaign (R1) conducted after Day 0, only 12 (18.5%) R1s were conducted by the target of 28 days after Day 0. Of the 89 OBRs with the second large-scale campaign (R2) conducted after Day 0, 30 (33.7%) R2s were conducted by the target of 56 days after Day 0. Twenty-three (31.9%) of the 72 outbreaks with isolates dated after Day 0 were stopped within the 120-day target. CONCLUSION: Since "the switch", delays in OBR implementation were evident in many countries, which may be related to the persistence of cVDPV2 outbreaks >120 days. To achieve timely and effective response, countries should follow GPEI OBR guidelines.

Despite exhaustive and fully-financed plans to manage the risks of globally coordinated cessation of oral poliovirus vaccine (OPV) containing type 2 (OPV2) prior to 2016, as of 2022, extensive, continued transmission of circulating vaccine-derived polioviruses (cVDPVs) type 2 (cVDPV2) remains. Notably, cumulative cases caused by cVDPV2 since 2016 now exceed 2,500. Earlier analyses explored the implications of using different vaccine formulations to respond to cVDPV2 outbreaks and demonstrated how different properties of novel OPV2 (nOPV2) might affect its performance compared to Sabin monovalent OPV2 (mOPV2). These prior analyses used fixed assumptions for how outbreak response would occur, but outbreak response implementation can change. We update an existing global poliovirus transmission model to explore different options for responding with different vaccines and assumptions about scope, delays, immunization intensity, target age groups, and number of rounds. Our findings suggest that in order to successfully stop all cVDPV2 transmission globally, countries and the Global Polio Eradication Initiative need to address the deficiencies in emergency outbreak response policy and implementation. The polio program must urgently act to substantially reduce response time, target larger populations - particularly in high transmission areas - and achieve high coverage with improved access to under-vaccinated subpopulations. Given the limited supplies of nOPV2 at the present, using mOPV2 intensively immediately, followed by nOPV2 intensively if needed and when sufficient quantities become available, substantially increases the probability of ending cVDPV2 transmission globally.

This study examined the impact of armed conflict on public health surveillance systems, the limitations of traditional surveillance in this context, and innovative strategies to overcome these limitations. A qualitative case study was conducted to examine the factors affecting the functioning of poliovirus surveillance in conflict-affected areas of Borno state, Nigeria using semi-structured interviews of a purposeful sample of participants. The main inhibitors of surveillance were inaccessibility, the destroyed health infrastructure, and the destroyed communication network. These three challenges created a situation in which the traditional polio surveillance system could not function. Three strategies to overcome these challenges were viewed by respondents as the most impactful. First, local community informants were recruited to conduct surveillance for acute flaccid paralysis in children in the inaccessible areas. Second, the informants engaged in local-level negotiation with the insurgency groups to bring children with paralysis to accessible areas for investigation and sample collection. Third, GIS technology was used to track the places reached for surveillance and vaccination and to estimate the size and location of the inaccessible population. A modified monitoring system tracked tailored indicators including the number of places reached for surveillance and the number of acute flaccid paralysis cases detected and investigated, and utilized GIS technology to map the reach of the program. The surveillance strategies used in Borno were successful in increasing surveillance sensitivity in an area of protracted conflict and inaccessibility. This approach and some of the specific strategies may be useful in other areas of armed conflict.

As of May 1, 2016, use of oral poliovirus vaccine (OPV) type 2 for routine and supplementary immunization activities ceased after a synchronized global switch from trivalent OPV (tOPV; containing Sabin strain types 1, 2, and 3) to bivalent OPV (bOPV; containing Sabin strain types 1 and 3) subsequent to the certified eradication of wild type poliovirus (WPV) type 2 in 2015 (1-3). Circulating vaccine-derived poliovirus (cVDPV) outbreaks* occur when transmission of Sabin strain poliovirus is prolonged in underimmunized populations, allowing viral genetic reversion to neurovirulence, resulting in cases of paralytic polio (1-3). Since the switch, monovalent OPV type 2 (mOPV2, containing Sabin strain type 2) has been used for response to cVDPV type 2 (cVDPV2) outbreaks; tOPV is used if cVDPV2 co-circulates with WPV type 1, and bOPV is used for cVDPV type 1 (cVDPV1) or type 3 (cVDPV3) outbreaks (1-4). In November 2020, the World Health Organization (WHO) Emergency Use Listing procedure authorized limited use of type 2 novel OPV (nOPV2), a vaccine modified to be more genetically stable than the Sabin strain, for cVDPV2 outbreak response (3,5). In October 2021, the Strategic Advisory Group of Experts on Immunization (WHO's principal advisory group) permitted wider use of nOPV2; however, current nOPV2 supply is limited (6). This report updates that of July 2019-February 2020 to describe global cVDPV outbreaks during January 2020-June 2021 (as of November 9, 2021)(†) (3). During this period, there were 44 cVDPV outbreaks of the three serotypes affecting 37 countries. The number of cVDPV2 cases increased from 366 in 2019 to 1,078 in 2020 (7). A goal of the Global Polio Eradication Initiative's (GPEI) 2022-2026 Strategic Plan is to better address the challenges to early CVDPV2 outbreak detection and initiate prompt and high coverage outbreak responses with available type 2 OPV to interrupt transmission by the end of 2023 (8).

BACKGROUND: World Health Organization African region is wild poliovirus-free; however, outbreaks of vaccine-derived poliovirus type 2 (VDPV2) continue to expand across the continent including in Chad. We conducted a serological survey of polio antibodies in polio high-risk areas of Chad to assess population immunity against poliovirus and estimate the risk of future outbreaks. METHODS: This was a community-based, cross-sectional survey carried out in September 2019. Children between 12 and 59 months were randomly selected using GIS enumeration of structures. Informed consent, demographic and anthropometric data, vaccination history, and blood spots were collected. Seropositivity against all 3 poliovirus serotypes was assessed using a microneutralization assay at Centers for Disease Control and Prevention, Atlanta, GA, USA. RESULTS: Analyzable data were obtained from 236 out of 285 (82.8%) enrolled children. Seroprevalence of polio antibodies for serotypes 1, 2, and 3 was 214/236 (90.7%); 145/236 (61.4%); and 196/236 (86.2%), respectively. For serotype 2, the seroprevalence significantly increased with age (P = .004); chronic malnutrition was a significant risk factor for being type 2-seronegative. INTERPRETATION: Poliovirus type 2 seroprevalence in young children was considered insufficient to protect against the spread of paralytic diseases caused by VDPV2. Indeed, VDPV2 outbreaks were reported from Chad in 2019 and 2020. High-quality immunization response to these outbreaks is needed to prevent further spread.

BACKGROUND:  Although patients who work and have related health issues are usually first seen in primary care, providers in these settings do not routinely ask questions about work. Guidelines to help manage such patients are rarely used in primary care. Electronic health record (EHR) systems with worker health clinical decision support (CDS) tools have potential for assisting these practices. OBJECTIVE:  This study aimed to identify the need for, and barriers and facilitators related to, implementation of CDS tools for the clinical management of working patients in a variety of primary care settings. METHODS:  We used a qualitative design that included analysis of interview transcripts and observational field notes from 10 clinics in five organizations. RESULTS:  We interviewed 83 providers, staff members, managers, informatics and information technology experts, and leaders and spent 35 hours observing. We identified eight themes in four categories related to CDS for worker health (operational issues, usefulness of proposed CDS, effort and time-related issues, and topic-specific issues). These categories were classified as facilitators or barriers to the use of the CDS tools. Facilitators related to operational issues include current technical feasibility and new work patterns associated with the coordinated care model. Facilitators concerning usefulness include users' need for awareness and evidence-based tools, appropriateness of the proposed CDS for their patients, and the benefits of population health data. Barriers that are effort-related include additional time this proposed CDS might take, and other pressing organizational priorities. Barriers that are topic-specific include sensitive issues related to health and work and the complexities of information about work. CONCLUSION:  We discovered several themes not previously described that can guide future CDS development: technical feasibility of the proposed CDS within commercial EHRs, the sensitive nature of some CDS content, and the need to assist the entire health care team in managing worker health.

In 2010, Nigeria adopted the use of web-based software District Health Information System, V.2 (DHIS2) as the platform for the National Health Management Information System. The platform supports real-time data reporting and promotes government ownership and accountability. To strengthen its routine immunisation (RI) component, the US Centers for Disease Control and Prevention (CDC) through its implementing partner, the African Field Epidemiology Network-National Stop Transmission of Polio, in collaboration with the Government of Nigeria, developed the RI module and dashboard and piloted it in Kano state in 2014. The module was scaled up nationally over the next 4 years with funding from the Bill & Melinda Gates Foundation and CDC. One implementation officer was deployed per state for 2 years to support operations. Over 60 000 RI healthcare workers were trained on data collection, entry and interpretation and each local immunisation officer in the 774 local government areas (LGAs) received a laptop and stock of RI paper data tools. Templates for national-level and state-level RI bulletins and LGA quarterly performance tools were developed to promote real-time data use for feedback and decision making, and enhance the performance of RI services. By December 2017, the DHIS2 RI module had been rolled out in all 36 states and the Federal Capital Territory, and all states now report their RI data through the RI Module. All states identified at least one government DHIS2 focal person for oversight of the system's reporting and management operations. Government officials routinely collect RI data and use them to improve RI vaccination coverage. This article describes the implementation process-including planning and implementation activities, achievements, lessons learnt, challenges and innovative solutions-and reports the achievements in improving timeliness and completeness rates.

Circulating vaccine-derived polioviruses (cVDPVs) can emerge in areas with low poliovirus immunity and cause outbreaks* of paralytic polio (1-5). Among the three types of wild poliovirus, type 2 was declared eradicated in 2015 (1,2). The use of trivalent oral poliovirus vaccine (tOPV; types 1, 2, and 3 Sabin strains) ceased in April 2016 via a 1-month-long, global synchronized switch to bivalent OPV (bOPV; types 1 and 3 Sabin strains) in immunization activities (1-4). Monovalent type 2 OPV (mOPV2; type 2 Sabin strain) is available for cVDPV type 2 (cVDPV2) outbreak response immunization (1-5). The number and geographic breadth of post-switch cVDPV2 outbreaks have exceeded forecasts that trended toward zero outbreaks 4 years after the switch and assumed rapid and effective control of any that occurred (4). New cVDPV2 outbreaks have been seeded by mOPV2 use, by both suboptimal mOPV2 coverage within response zones and recently mOPV2-vaccinated children or contacts traveling outside of response zones, where children born after the global switch are fully susceptible to poliovirus type 2 transmission (2-4). In addition, new emergences can develop by inadvertent exposure to Sabin OPV2-containing vaccine (i.e., residual response mOPV2 or tOPV) (4). This report updates the January 2018-June 2019 report with information on global cVDPV outbreaks during July 2019-February 2020 (as of March 25, 2020)(dagger) (2). Among 33 cVDPV outbreaks reported during July 2019-February 2020, 31 (94%) were cVDPV2; 18 (58%) of these followed new emergences. In mid-2020, the Global Polio Eradication Initiative (GPEI) plans to introduce a genetically stabilized, novel OPV type 2 (nOPV2) that has a lower risk for generating VDPV2 than does Sabin mOPV2; if nOPV2 is successful in limiting new VDPV2 emergences, GPEI foresees the replacement of Sabin mOPV2 with nOPV2 for cVDPV2 outbreak responses during 2021 (2,4,6).

BACKGROUND: Four wild polio-virus cases were reported in Borno State, Nigeria 2016, 1 year after Nigeria had been removed from the list of polio endemic countries by the World Health Organization. Resulting from Nigeria's decade long conflict with Boko Haram, health officials had been unable to access as much as 60% of the settlements in Borno, hindering vaccination and surveillance efforts. This lack of accessibility made it difficult for the government to assess the current population distribution within Borno. This study aimed to use high resolution, visible band satellite imagery to assess the habitation of inaccessible villages in Borno State. METHODS: Using high resolution (31-50 cm) imagery from DigitalGlobe, analysts evaluated the habitation status of settlements in Borno State identified by Nigeria's Vaccination Tracking System. The analysts looked at imagery of each settlement and, using vegetation (overgrowth vs. cleared) as a proxy for human habitation, classified settlements into three categories: inhabited, partially abandoned, and abandoned. Analysts also classified the intact percentage of each settlement starting at 0% (totally destroyed since last assessment) and increasing in 25% intervals through 100% (completely intact but not expanded) up to 200+% (more than doubled in size) by looking for destroyed buildings. These assessments were then used to adjust previously established population estimates for each settlement. These new population distributions were compared to vaccination efforts to determine the number of children under 5 unreached by vaccination teams. RESULTS: Of the 11,927 settlements assessed 3203 were assessed as abandoned (1892 of those completely destroyed), 662 as partially abandoned, and 8062 as fully inhabited as of December of 2017. Comparing the derived population estimates from the new assessments to previous assessment and the activities of vaccination teams shows that an estimated 180,155 of the 337,411 under five children who were unreached in 2016 were reached in 2017 (70.5% through vaccination efforts in previously inaccessible areas, 29.5% through displacement to accessible areas). CONCLUSIONS: This study's methodology provides important planning and situation awareness information to health workers in Borno, Nigeria, and may serve as a model for future data gathering efforts in inaccessible regions.

Widespread use of live attenuated (Sabin) oral poliovirus vaccine (OPV) has resulted in marked progress toward global poliomyelitis eradication (1). However, in underimmunized populations, extensive person-to-person transmission of Sabin poliovirus can result in genetic reversion to neurovirulence and paralytic vaccine-derived poliovirus (VDPV) disease (1). This report updates (as of February 26, 2019) previous reports on circulating VDPV type 2 (cVDPV2) outbreaks during 2017-2018 in the Democratic Republic of the Congo (DRC) and in Somalia, which experienced a concurrent cVDPV type 3 (cVDPV3) outbreak* (2,3). In DRC, 42 cases have been reported in four cVDPV2 outbreaks; paralysis onset in the most recent case was October 7, 2018 (2). Challenges to interrupting transmission have included delays in outbreak-response supplementary immunization activities (SIAs) and difficulty reaching children in all areas. In Somalia, cVDPV2 and cVDPV3 were detected in sewage before the detection of paralytic cases (3). Twelve type 2 and type 3 cVDPV cases have been confirmed; the most recent paralysis onset dates were September 2 (cVDPV2) and September 7, 2018 (cVDPV3). The primary challenge to interrupting transmission is the residence of >300,000 children in areas that are inaccessible for vaccination activities. For both countries, longer periods of surveillance are needed before interruption of cVDPV transmission can be inferred.

Bangladesh introduced hepatitis B vaccine in a phased manner during 2003-2005 into the routine childhood vaccination schedule. This study was designed to evaluate the impact of the introduction of hepatitis B vaccine in Bangladesh by comparing hepatitis B surface antigen (HBsAg) prevalence among children born before and after vaccine introduction and to estimate the risk of vertical transmission of chronic hepatitis B virus (HBV) infection from mother to infant. We also evaluated the field sensitivity and specificity of an HBsAg point-of-care test strip. We selected a nationally representative sample of 2,100 prevaccine era and 2,100 vaccine era children. We collected a 5-mL blood sample from each child. One drop of blood was used to perform rapid HBsAg testing. If a child had a positive HBsAg test result with the rapid test, a blood sample was collected from the mother of the HBsAg-positive child and from the mothers of two subsequently enrolled HBsAg-negative children. All samples were tested for serologic markers of HBV infection using standard enzyme-linked immunosorbent assay. One (0.05%) child in the vaccine era group and 27 (1.2%; 95% confidence interval [CI]: 0.8-1.7%) children in the prevaccine era group were HBsAg positive. Mothers of HBsAg-positive children were more likely to be HBsAg positive than mothers of HBsAg-negative children (odds ratios = 4.7; 95% CI: 1.0-21.7%). Sensitivity of the HBsAg rapid test was 91.2% (95% CI: 76.6-98.1%) and specificity was 100% (95% CI: 99.9-100%). The study results suggest that even without a birth dose, the hepatitis B vaccine program in Bangladesh was highly effective in preventing chronic HBV infection among children.

Nearly three decades after the World Health Assembly launched the Global Polio Eradication Initiative in 1988, four of the six World Health Organization (WHO) regions have been certified polio-free (1). Nigeria is one of three countries, including Pakistan and Afghanistan, where wild poliovirus (WPV) transmission has never been interrupted. In September 2015, after >1 year without any reported WPV cases, Nigeria was removed from WHO's list of countries with endemic WPV transmission (2); however, during August and September 2016, four type 1 WPV (WPV1) cases were reported from Borno State, a state in northeastern Nigeria experiencing a violent insurgency (3). The Nigerian government, in collaboration with partners, launched a large-scale coordinated response to the outbreak (3). This report describes progress in polio eradication activities in Nigeria during January-December 2017 and updates previous reports (3-5). No WPV cases have been reported in Nigeria since September 2016; the latest case had onset of paralysis on August 21, 2016 (3). However, polio surveillance has not been feasible in insurgent-controlled areas of Borno State. Implementation of new strategies has helped mitigate the challenges of reaching and vaccinating children living in security-compromised areas, and other strategies are planned. Despite these initiatives, however, approximately 130,000-210,000 (28%-45%) of the estimated 469,000 eligible children living in inaccessible areas in 2016 have not been vaccinated. Sustained efforts to optimize surveillance and improve immunization coverage, especially among children in inaccessible areas, are needed.

Vaccination is an important and cost-effective disease prevention and control strategy. Despite progress in vaccine development and immunization delivery systems worldwide, populations in areas of conflict (hereafter, "conflict settings") often have limited or no access to lifesaving vaccines, leaving them at increased risk for morbidity and mortality related to vaccine-preventable disease. Without developing and refining approaches to reach and vaccinate children and other vulnerable populations in conflict settings, outbreaks of vaccine-preventable disease in these settings may persist and spread across subnational and international borders. Understanding and refining current approaches to vaccinating populations in conflict and humanitarian emergency settings may save lives. Despite major setbacks, the Global Polio Eradication Initiative has made substantial progress in vaccinating millions of children worldwide, including those living in communities affected by conflicts and other humanitarian emergencies. In this article, we examine key strategic and operational tactics that have led to increased polio vaccination coverage among populations living in diverse conflict settings, including Nigeria, Somalia, and Pakistan, and how these could be applied to reach and vaccinate populations in other settings across the world.

From 2012 to date, Nigeria has been the focus of intensified polio eradication efforts. Large investments made by multiple partner organizations and the federal Ministry of Health to support strategies and resources, including personnel, for increasing vaccination coverage and improved performance monitoring paid off, as the number of wild poliovirus (WPV) cases detected in Nigeria were reduced significantly, from 122 in 2012 to 6 in 2014. No WPV cases were detected in Nigeria in 2015 and as at March 2017, only 4 WPV cases had been detected. Given the momentum gained toward polio eradication, these resources seem well positioned to help advance other priority health agendas in Nigeria, particularly the control of vaccine-preventable diseases, such as measles. Despite implementation of mass measles vaccination campaigns, measles outbreaks continue to occur regularly in Nigeria, leading to high morbidity and mortality rates for children <5 years of age. The National Stop Transmission of Polio (NSTOP) program was collaboratively established in 2012 to create a network of staff working at national, state, and district levels in areas deemed high risk for vaccine-preventable disease outbreaks. As an example of how the polio legacy can create long-lasting improvements to public health beyond polio, the Centers for Disease Control and Prevention will transition >180 NSTOP officers to provide technical experience to improve measles surveillance, routine vaccination coverage, and outbreak investigation and response in high-risk areas.