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When the Global Polio Eradication Initiative began in 1988, wild poliovirus (WPV) transmission was occurring in 125 countries; currently, only WPV type 1 (WPV1) transmission continues, and as of August 2021, WPV1 transmission persists in only two countries (1,2). This report describes Pakistan's progress toward polio eradication during January 2020-July 2021 and updates previous reports (3,4). In 2020, Pakistan reported 84 WPV1 cases, a 43% reduction from 2019; as of August 25, 2021, Pakistan has reported one WPV1 case in 2021. Circulating vaccine-derived poliovirus (cVDPV) emerges as a result of attenuated oral poliovirus vaccine (OPV) virus regaining neurovirulence after prolonged circulation in underimmunized populations and can lead to paralysis. In 2019, 22 cases of cVDPV type 2 (cVDPV2) were reported in Pakistan, 135 cases were reported in 2020, and eight cases have been reported as of August 25, 2021. Because of the COVID-19 pandemic, planned supplementary immunization activities (SIAs)* were suspended during mid-March-June 2020 (3,5). Seven SIAs were implemented during July 2020-July 2021 without substantial decreases in SIA quality. Improving the quality of polio SIAs, vaccinating immigrants from Afghanistan, and implementing changes to enhance program accountability and performance would help the Pakistan polio program achieve its goal of interrupting WPV1 transmission by the end of 2022., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. No potential conflicts of interest were disclosed.

Since October 2016, Afghanistan and Pakistan have been the only countries with reported cases of wild poliovirus type 1 (WPV1) (1). In Afghanistan, although the number of cases had declined during 2013-2016, the polio eradication program experienced challenges during 2017-2019. This report describes polio eradication activities and progress in Afghanistan during January 2018-May 2019 and updates previous reports (2,3). During May-December 2018, insurgent groups (antigovernment elements) banned house-to-house vaccination in most southern and southeastern provinces, leaving approximately 1 million children inaccessible to oral poliovirus vaccine (OPV) administration. During January-April 2019, vaccination targeting children at designated community sites (site-to-site vaccination) was permitted; however, at the end of April 2019, vaccination campaigns were banned nationally. During 2018, a total of 21 WPV1 cases were reported in Afghanistan, compared with 14 during 2017. During January-May 2019, 10 WPV1 cases were reported (as of May 31), compared with eight during January-May 2018. Sewage sample-testing takes place at 20 sites in the highest-risk areas for poliovirus circulation; 17 have detected WPV1 since January 2017, primarily in the southern and eastern provinces. Continued discussion with antigovernment elements to resume house-to-house campaigns is important to achieving polio eradication in Afghanistan. To increase community support for vaccination, collaboration among humanitarian service agencies to address other urgent health and basic needs is critical., Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. No potential conflicts of interest were disclosed.

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., Competing Interests: All authors have completed and submitted the ICMJE form for disclosure of potential conflicts of interest. No potential conflicts of interest were disclosed.

Afghanistan, Pakistan, and Nigeria remain the only countries where transmission of endemic wild poliovirus type 1 (WPV1) continues (1). This report describes polio eradication activities, progress, and challenges to eradication in Afghanistan during January 2017-May 2018 and updates previous reports (2, 3). Fourteen WPV1 cases were confirmed in Afghanistan in 2017, compared with 13 in 2016; during January-May 2018, eight WPV1 cases were reported, twice the number reported during January-May 2017. To supplement surveillance for acute flaccid paralysis (AFP) and laboratory testing of stool samples, environmental surveillance (testing of sewage samples) was initiated in 2013 and includes 20 sites, 15 of which have detected WPV1 circulation. The number of polio-affected districts increased from six in 2016 to 14 in 2017 (including WPV1 cases and positive environmental samples). Access to children for supplementary immunization activities (SIAs) (mass campaigns targeting children aged <5 years with oral poliovirus vaccine [OPV], regardless of vaccination history), which improved during 2016 to early 2018, worsened in May 2018 in security-challenged areas of the southern and eastern regions. To achieve WPV1 eradication, measures to maintain and regain access for SIAs in security-challenged areas, strengthen oversight of SIAs in accessible areas to reduce the number of missed children, and coordinate with authorities in Pakistan to track and vaccinate mobile populations at high risk in their shared transit corridors must continue., Competing Interests: No conflicts of interest were reported.

Since the 1988 inception of the Global Polio Eradication Initiative (GPEI), progress toward interruption of wild poliovirus (WPV) transmission has occurred mostly through extensive use of oral poliovirus vaccine (OPV) in mass vaccination campaigns and through routine immunization services (1,2). However, because OPV contains live, attenuated virus, it carries the rare risk for reversion to neurovirulence. In areas with very low OPV coverage, prolonged transmission of vaccine-associated viruses can lead to the emergence of vaccine-derived polioviruses (VDPVs), which can cause outbreaks of paralytic poliomyelitis. Although WPV type 2 has not been detected since 1999, and was declared eradicated in 2015,* most VDPV outbreaks have been attributable to VDPV serotype 2 (VDPV2) (3,4). After the synchronized global switch from trivalent OPV (tOPV) (containing vaccine virus types 1, 2, and 3) to bivalent OPV (bOPV) (types 1 and 3) in April 2016 (5), GPEI regards any VDPV2 emergence as a public health emergency (6,7). During May-June 2017, VDPV2 was isolated from stool specimens from two children with acute flaccid paralysis (AFP) in Deir-ez-Zor governorate, Syria. The first isolate differed from Sabin vaccine virus by 22 nucleotides in the VP1 coding region (903 nucleotides). Genetic sequence analysis linked the two cases, confirming an outbreak of circulating VDPV2 (cVDPV2). Poliovirus surveillance activities were intensified, and three rounds of vaccination campaigns, aimed at children aged <5 years, were conducted using monovalent OPV type 2 (mOPV2). During the outbreak, 74 cVDPV2 cases were identified; the most recent occurred in September 2017. Evidence indicates that enhanced surveillance measures coupled with vaccination activities using mOPV2 have interrupted cVDPV2 transmission in Syria., Competing Interests: No conflicts of interest were reported.

Following the declaration of eradication of wild poliovirus (WPV) type 2 in September 2015, trivalent oral poliovirus vaccine (tOPV) was withdrawn globally to reduce the risk for type 2 vaccine-derived poliovirus (VDPV2) transmission; all countries implemented a synchronized switch to bivalent OPV (type 1 and 3) in April 2016 (1,2). Any isolation of VDPV2 after the switch is to be treated as a potential public health emergency and might indicate the need for supplementary immunization activities (3,4). On August 9, 2016, VDPV2 was isolated from a sewage sample taken from an environmental surveillance site in Hyderabad, Sindh province, Pakistan. Possible vaccination activities in response to VDPV2 isolation include the use of injectable inactivated polio vaccine (IPV), which poses no risk for vaccine-derived poliovirus transmission. Fractional-dose, intradermal IPV (fIPV), one fifth of the standard intramuscular dose, has been developed to more efficiently manage limited IPV supplies. fIPV has been shown in some studies to be noninferior to full-dose IPV (5,6) and was used successfully in response to a similar detection of a single VDPV2 isolate from sewage in India (7). Injectable fIPV was used for response activities in Hyderabad and three neighboring districts. This report describes the findings of an assessment of preparatory activities and subsequent implementation of the fIPV campaign. Despite achieving high coverage (>80%), several operational challenges were noted. The lessons learned from this campaign could help to guide the planning and implementation of future fIPV vaccination activities.

In 1988, the World Health Assembly launched the Global Polio Eradication Initiative. Among the three wild poliovirus serotypes, only wild poliovirus (WPV) type 1 (WPV1) has been detected since 2012. Since 2014, Pakistan, Afghanistan, and Nigeria remain the only countries with continuing endemic WPV1 transmission. This report describes activities conducted and progress made toward the eradication of poliovirus in Pakistan during January 2016-July 2017 and provides an update to previous reports (1,2). In 2016, Pakistan reported 20 WPV1 cases, a 63% decrease compared with 54 cases in 2015 (3). As of September 25, 2017, five WPV1 cases have been reported in 2017, representing a 69% decline compared with 16 cases reported during the same period in 2016 (Figure 1). During January-September 2017, WPV1 was detected in 72 of 468 (15%) environmental samples collected, compared with 36 of 348 (9%) samples collected during the same period in 2016. WPV1 was detected in environmental samples in areas where no polio cases are being reported, which indicates that WPV1 transmission is continuing in some high-risk areas. Interruption of WPV transmission in Pakistan requires maintaining focus on reaching missed children (particularly among mobile populations), continuing community-based vaccination, implementing the 2017-2018 National Emergency Action Plan (4), and improving routine immunization services.

Afghanistan, Pakistan, and Nigeria remain the only countries where the transmission of endemic wild poliovirus type 1 (WPV1) continues (1). This report describes polio eradication activities, progress, and challenges in Afghanistan during January 2016-June 2017 and updates previous reports (2,3). Thirteen WPV1 cases were confirmed in Afghanistan in 2016, a decrease of seven from the 20 cases reported in 2015. From January to June 2017, five WPV1 cases were reported, compared with six during the same period in 2016. The number of affected districts declined from 23 (including WPV1-positive acute flaccid paralysis [AFP] cases and positive environmental sewage samples) in 2015 to six in 2016. To achieve WPV1 eradication, it is important that Afghanistan's polio program continue to collaborate with that of neighboring Pakistan to track and vaccinate groups of high-risk mobile populations and strengthen efforts to reach children in security-compromised areas.

As the world advances toward the eradication of polio, outbreaks of wild poliovirus (WPV) in polio-free regions pose a substantial risk to the timeline for global eradication. Countries and regions experiencing active conflict, chronic insecurity, and large-scale displacement of persons are particularly vulnerable to outbreaks because of the disruption of health care and immunization services (1). A polio outbreak occurred in the Middle East, beginning in Syria in 2013 with subsequent spread to Iraq (2). The outbreak occurred 2 years after the onset of the Syrian civil war, resulted in 38 cases, and was the first time WPV was detected in Syria in approximately a decade (3,4). The national governments of eight countries designated the outbreak a public health emergency and collaborated with partners in the Global Polio Eradication Initiative (GPEI) to develop a multiphase outbreak response plan focused on improving the quality of acute flaccid paralysis (AFP) surveillance* and administering polio vaccines to >27 million children during multiple rounds of supplementary immunization activities (SIAs). † Successful implementation of the response plan led to containment and interruption of the outbreak within 6 months of its identification. The concerted approach adopted in response to this outbreak could serve as a model for responding to polio outbreaks in settings of conflict and political instability.

Only 74 cases of wild poliovirus (WPV) were reported globally in 2015, the lowest number of cases ever reported worldwide (1,2). All of the reported cases were WPV type 1 (WPV1), the only known WPV type still circulating; WPV type 2 has been eradicated, and WPV type 3 has not been detected since November 2012 (1). In 2015 in Afghanistan, WPV detection also declined from 2014, and trends observed in 2016 suggest that circulation of the virus is limited to a few localized areas. Despite the progress, there are concerns about the ability of the country's Polio Eradication Initiative (PEI) to meet the goal of interrupting endemic WPV transmission by the end of 2016 (3). The deteriorating security situation in the Eastern and Northeastern regions of the country considerably limits the ability to reach and vaccinate children in these regions. Furthermore, because of frequent population movements to and from Pakistan, cross-border transmission of WPV1 continues (4). Although the national PEI has taken steps to improve the quality of supplementary immunization activities (SIAs),* significant numbers of children living in accessible areas are still being missed during SIAs, and routine immunization services remain suboptimal in many parts of the country. This report describes polio eradication activities and progress in Afghanistan during January 2015‒August 2016 and updates previous reports (5,6). During 2015, a total of 20 WPV1 cases were reported in Afghanistan, compared with 28 cases in 2014; eight cases were reported during January‒August 2016, compared with nine cases reported during the same period in 2015. To achieve interruption of poliovirus transmission in Afghanistan, it is important that the 2016-2017 National Emergency Action Plan † for polio eradication be systematically implemented, including 1) improving the quality of SIAs and routine immunization services, 2) ensuring ongoing dialogue between PEI leaders and local authorities, 3) adopting innovative strategies for reaching children in security-compromised and inaccessible areas, and 4) strengthening cross-border coordination of polio vaccination and surveillance activities with Pakistan.

Despite recent progress toward global polio eradication, endemic transmission of wild poliovirus (WPV) continues to be reported in Afghanistan and Pakistan. The Afghanistan program must overcome many challenges to remain on track toward achieving the objectives set in the 2013–2018 strategic plan of the Global Polio Eradication Initiative (GPEI). Cross-border transmission of WPV type 1 (WPV1) continues to occur among children traveling to and from Pakistan. The country's routine immunization system remains weak and unable to reach recommended benchmarks in most regions; hence, the national Polio Eradication Initiative (PEI) relies mainly on providing children aged <5 years with oral poliovirus vaccine (OPV), administered during supplementary immunization activities (SIAs). Because of ongoing conflict and insecurity, some children continue to be missed during SIAs in areas not under government control; however, the majority of missed children live in accessible areas and are often unreached because of a failure to plan, implement, and supervise SIAs efficiently. This report describes polio eradication activities and progress in Afghanistan during January 2014‒August 2015 and updates previous reports. During 2014, a total of 28 WPV1 cases were reported in Afghanistan, compared with 14 cases in 2013; nine cases were reported during January‒August 2015, the same number as during the same period in 2014. To eliminate poliovirus transmission in Afghanistan, emergency operations centers (EOCs) need to be established at the national level and in critical regions without delay to improve overall coordination and oversight of polio eradication activities. The recently revised National Emergency Action Plan for polio eradication needs to be fully implemented, including detailed microplanning and enhanced monitoring and supervision of SIAs, as well as improved cross-border coordination with Pakistan.