Progress Toward Poliomyelitis Eradication — Nigeria, January 2018–May 2019

The number of wild poliovirus (WPV) cases in Nigeria decreased from 1,122 in 2006 to six WPV type 1 (WPV1) in 2014 (1). During August 2014-July 2016, no WPV cases were detected; during August-September 2016, four cases were reported in Borno State. An insurgency in northeastern Nigeria had resulted in 468,800 children aged <5 years deprived of health services in Borno by 2016. Military activities in mid-2016 freed isolated families to travel to camps, where the four WPV1 cases were detected. Oral poliovirus vaccine (OPV) campaigns were intensified during August 2016-December 2017; since October 2016, no WPV has been detected (2). Vaccination activities in insurgent-held areas are conducted by security forces; however, 60,000 unvaccinated children remain in unreached settlements. Since 2018, circulating vaccine-derived poliovirus type 2 (cVDPV2) has emerged and spread from Nigeria to Niger and Cameroon; outbreak responses to date have not interrupted transmission. This report describes progress in Nigeria polio eradication activities during January 2018-May 2019 and updates the previous report (2). Interruption of cVDPV2 transmission in Nigeria will need increased efforts to improve campaign quality and include insurgent-held areas. Progress in surveillance and immunization activities will continue to be reviewed, potentially allowing certification of interruption of WPV transmission in Africa in 2020.

The number of wild poliovirus (WPV) cases in Nigeria decreased from 1,122 in 2006 to six WPV type 1 (WPV1) in 2014 (1). During August 2014-July 2016, no WPV cases were detected; during August-September 2016, four cases were reported in Borno State. An insurgency in northeastern Nigeria had resulted in 468,800 children aged <5 years deprived of health services in Borno by 2016. Military activities in mid-2016 freed isolated families to travel to camps, where the four WPV1 cases were detected. Oral poliovirus vaccine (OPV) campaigns were intensified during August 2016-December 2017; since October 2016, no WPV has been detected (2). Vaccination activities in insurgent-held areas are conducted by security forces; however, 60,000 unvaccinated children remain in unreached settlements. Since 2018, circulating vaccine-derived poliovirus type 2 (cVDPV2) has emerged and spread from Nigeria to Niger and Cameroon; outbreak responses to date have not interrupted transmission. This report describes progress in Nigeria polio eradication activities during January 2018-May 2019 and updates the previous report (2). Interruption of cVDPV2 transmission in Nigeria will need increased efforts to improve campaign quality and include insurgent-held areas. Progress in surveillance and immunization activities will continue to be reviewed, potentially allowing certification of interruption of WPV transmission in Africa in 2020.

Security Situation
A violent insurgency that arose in 2009 and was followed by insurgents seizing territory beginning in 2012 in Borno, Adamawa, and Yobe states (and bordering areas of Cameroon, Chad, and Niger) led to the internal displacement of 1.8 million persons (3). By 2016, this conflict created a humanitarian crisis in which an estimated 468,800 children aged <5 years resided in insurgent-held areas in Borno with no health services, including vaccination and surveillance activities (2). Since December 2016, movement of populations within and out of Borno insurgent-held areas has continued with increasing numbers of persons now living in areas outside insurgents' control; however, many settlements remain inaccessible (Figure).

Routine Childhood Immunization
National coverage levels for the third dose of poliovirus vaccine (Pol3) delivered through routine immunization services by age 12 months have been <60% since 2002,* with lower rates in northern states. A 2016 survey indicated that Pol3 coverage nationally was 33% and <25% in seven of 13 northern states (4).

Poliovirus Surveillance
Acute flaccid paralysis surveillance. The quality of polio surveillance is assessed by nonpolio AFP (NPAFP) rates and stool collection adequacy. † Targets for Nigeria are an NPAFP rate of three or more cases per 100,000 population aged <15 years per year and stool collection adequacy ≥80% of AFP cases. In 2018, the national NPAFP rate was 9.6, and stool adequacy was 95%. As of May 31, 2019, the annualized national 2019 NPAFP rate was 8.0, and stool adequacy was 95%. In Borno, in 2018, the NPAFP rate was 24.5 with 85% stool adequacy; the annualized 2019 NPAFP rate is 19.6 and stool adequacy is 87%.
The destruction of health facilities after the insurgency disrupted health facility-based surveillance in Borno. Community informants help identify AFP cases in insurgentheld areas in Borno, particularly since February 2018. As of May 31, 2019, a total of 1,018 community informants in Borno reported 220 verified AFP cases during 2018-2019. Stool specimens are obtained when patients with AFP and their families temporarily leave insurgent-held areas for evaluation in safe areas; in 2018, stool adequacy for these AFP cases was 61% and in 2019, 79% to date.
Environmental surveillance. To supplement AFP surveillance, sewage samples are tested for polioviruses (5
Emergence in Jigawa State. Eight cVDPV2-positive sewage samples collected during January 10-October 17, 2018, in Jigawa were genetically linked to four cVDPV2 cases with paralysis onset during April 15-October 13, 2018. This outbreak has spread to 11 other states, totaling 41 cVDPV2 cases and 71 sewage isolates. Genetically related poliovirus was also isolated from 11 AFP patients in Niger Republic, with onset

Vaccination Activities
In 2018, two national supplementary immunization activities (SIAs) § with bOPV, one subnational SIA with bOPV in five states, two subnational SIAs in seven states using bOPV and fractional IPV, and three subnational SIAs in two states using bOPV and fractional IPV were conducted. One subnational SIA using bOPV has been conducted in seven states to date in 2019. Two subnational SIAs were conducted in two states using bOPV and fractional IPV. Gombe was the only state with three subnational SIAs to date in 2019 (Table 2).
Since December 2016, little change has occurred in the areas not accessible by standard house-to-house SIA teams in Borno. Two novel approaches for immunizing children in insurgentheld areas in Borno were implemented (2). Reaching Every Settlement utilizes security escorts to enable vaccinators to § SIAs are mass immunization campaigns conducted over several days to boost population immunity in areas with weak routine childhood immunization services and suboptimal coverage. The goal of SIAs is to reach every child aged <5 years with OPV, regardless of their vaccination status. http://polioeradication. org/who-we-are/strategic-plan-2013-2018/supplementary-immunization/.
reach children in some settlements in insurgent-held areas, and Reaching Inaccessible Children enables vaccination of children by trained military personnel in settlements only accessible by these personnel (2). Satellite imagery is used to estimate population sizes in settlements and vaccination team movements are tracked using geographic information systems, providing data on geographic reach by these immunization approaches (Figure).  Table 2). The quality of outbreak response SIAs as assessed by post-campaign lot quality assurance sampling surveys has been variable; the national average for mOPV2 SIAs ranged from 64% to 90% of sampled local government areas reaching the target 90% threshold of   mOPV2  bOPV  bOPV + fIPV  mOPV2   Abia  2  -**  ------Adamawa  4  -1  1  -2  May 4  80-100  Akwa Ibom  2  -------Anambra  2  -------Bauchi  3  1  5  1  -2  May 4  73-100  Bayelsa  2  -------Benue  2  -1  --1  Jan 26  89-100  Borno  4  1  2  1  -1 May 25 87-100 Cross River   (2), even as previously silent areas in Borno have incrementally increased surveillance with community informants. Progress in decreasing the number of unvaccinated children in insurgent-held areas resulted from improved vaccination reach by novel approaches and net population migration from insurgent-held areas to accessible areas. Additional surveillance sensitivity assessments in Nigeria and other African countries are underway, potentially to allow certification of interruption of WPV transmission by the African Regional Certification Commission in 2020. However, active cVDPV2 transmission continuing into 2020 in Nigeria or eight other

Summary
What is already known about this topic?
The latest wild poliovirus (WPV) case in Nigeria occurred in August 2016 and was reported in September 2016, in Borno State.
What is added by this report?
The number of children living in insurgent-held areas in Borno who have not had access to poliovirus vaccines was reduced by 87% during December 2016-May 2017. Trained community members living in insurgent-held areas have reported suspected polio cases with no WPV identified on virologic testing, which suggests that WPV transmission might have been interrupted in Nigeria. However, outbreaks caused by type 2 circulating vaccine-derived poliovirus (cVDPV2) are spreading internationally.
What are the implications for public health practice? Improved polio mass campaign quality is required to achieve interruption of all cVDPV2 transmission in Nigeria.
countries on the continent with active cVDPV2 outbreaks might complicate the certification process.
Nigeria experienced multiple cVDPV2 outbreaks during 2005-2015 as well as ongoing transmission after cVDPV2 importation in 2013 because of vulnerability to emergence and spread of cVDPV2 from the predominant use of mOPV1, mOPV3 and bOPV during 2005-2014 SIAs, coupled with chronically low routine tOPV coverage (6). In addition, tOPV SIAs before the tOPV-to-bOPV switch were not sufficiently effective in all areas.
Children remaining in insurgent-held areas of Borno have remained inaccessible to mOPV2 administration by standard house-to-house SIAs for the cVDPV2 outbreak response; administration of mOPV2 in those areas will require Reaching Every Settlement and Reaching Inaccessible Children. Although mOPV2 is the tool to stop cVDPV2 outbreaks, it also carries the risk of seeding new emergences of cVDPV2 in areas with low-quality SIAs. Increased efforts for appropriate planning and supervision of subsequent SIAs will be important in ensuring optimal response quality necessary to interrupt cVDPV2 transmission and emergence.