Progress Toward Poliomyelitis Eradication ― Afghanistan, January 2021–September 2022

Immunization Activities

The World Health Organization (WHO) and UNICEF estimate of national 2021 immunization coverage with 3 doses of oral poliovirus vaccine (OPV3) among children aged 12–23 months was 71% compared with 75% in 2020. The estimated 1-dose coverage with injectable inactivated poliovirus vaccine was 67% in 2021 compared with 62% in 2020 (5). However, these national estimates obscure substantial subnational coverage gaps.

Because of the low quality of routine immunization (RI) data, caregiver recall dose history from investigations of acute flaccid paralysis (AFP) in children who do not have laboratory evidence of poliovirus infection (nonpolio AFP [NPAFP]) is used as a proxy for RI coverage. Among the 2,567 infants and children aged 6–59 months with NPAFP in 2021, 68% had received ≥3 RI OPV doses nationwide; 17% had not received any RI dose. In 2022, as of August 31, these percentages were similar (67% and 17%, respectively). In 2021, 4% of children with NPAFP had not received any OPV through RI or SIAs (zero-dose children); the percentage of zero-dose children declined to 2% in 2022. By province, the highest percentages of zero-dose children in 2021 were reported from Zabul (28%) and Helmand (17%) provinces in the South Region, and from Nuristan (11%) in the East Region in 2022, as of August 31.

In 2015, WHO declared wild poliovirus type 2 to be eradicated.^§ In 2016, Afghanistan joined OPV-using countries around the world in implementing a synchronized withdrawal of trivalent OPV (tOPV), containing Sabin-strain types 1, 2, and 3, and replacement with bivalent OPV (bOPV), containing Sabin-strain types 1 and 3, and ≥1 dose of inactivated poliovirus vaccine as part of containment efforts for all type 2 polioviruses (6). However, in 2020 when Afghanistan began to report both cVDPV2 and WPV1 polio cases, the Global Polio Eradication Initiative authorized the use of tOPV for outbreak response. During January–December 2021, five SIAs were conducted, including two after the political transition; all were national immunization days (NIDs). During January–September 2022, nine SIAs targeting children aged <5 years were conducted: six NIDs, one subnational immunization day, and two large-scale SIAs conducted in response to a polio case (case-response SIAs). The NIDs conducted in January, March, November, and December 2021 used tOPV; the remaining SIAs in 2021 and 2022 used bOPV.

In November 2021, during the first SIA after the political transition, only 53% of the 10 million children targeted by SIAs lived in areas without any restriction on how SIAs were conducted. This percentage gradually increased and reached 76% by the September 2022 NID. The reported NID OPV coverage in areas where SIAs were conducted without restrictions increased from 72% in June 2021 to approximately 100% in March, May, and June 2022, although this figure likely overestimates true coverage because of poor target setting and data management. Reported coverage was <50% in districts with restrictions on SIA implementation. In 2022, to date, the program has reached 3.5–4.5 million children previously unreachable because the insurgency prevented access before the government transition.

Lot quality assurance sampling (LQAS)^¶ surveys are conducted to assess SIA quality. Previously limited in implementation, these surveys were expanded nationwide in 2022 to include all districts. During the first five 2022 NIDs, 1,319 lots were assessed, a 65% increase over the 797 assessed during 2021, and the quality of implementing LQAS surveys improved. More lots were reported as failed at the 90% SIA coverage threshold in 2022 (37%) than in 2021 (18%); however, the primary reason was that approximately all lots in districts where SIA implementation methods were restricted failed LQAS assessments.

Poliovirus Surveillance

AFP surveillance. The Afghanistan AFP surveillance network comprises 1,947 active surveillance sites (visited by surveillance officers), 3,222 zero-reporting sites with passive monthly reporting, and 46,000 community-based reporting volunteers. Detection of two or more NPAFP cases per 100,000 persons aged <15 years** along with collection of adequate stool specimens^†† from ≥80% of AFP cases indicates that surveillance is sufficiently sensitive to detect a case of paralytic polio. During 2021, the national NPAFP rate was 19 per 100,000 persons aged <15 years (regional range = 12–26); during January–August 2022, the annualized NPAFP rate was 25 (regional range = 17–40). The percentage of AFP cases with adequate specimens was 94% in 2021 and 95% to date in 2022 (regional range = 90%–98% in 2021 and 92%–98% in 2022) (Table).

Environmental surveillance. Poliovirus surveillance in Afghanistan is supplemented by environmental surveillance (ES), the systematic sampling and virologic testing of sewage at 30 sites in 13 provinces. In 2021, only one WPV1 sample was detected among ES samples from the Helmand province in the South Region. As of October 20, 2022, WPV1 was detected during the reporting period in three sites: one in Nangarhar and two in Kunar provinces in the East Region, with the latest from a site in Kunar province in September 2022. During 2021, cVDPV2 was isolated from 40 ES specimens from Helmand, Herat, Kabul, Kandahar, Kunduz, and Nangarhar provinces; the latest isolation was from an ES sample collected in June 2021 in Kandahar province.

Epidemiology of Polio Cases and Genomic Sequence Analysis of Poliovirus Isolates

Four WPV1 cases were detected in 2021, one from Ghazni province in the Southeast Region and three from Kunduz province in the Northeast Region. During January–September 2022 (as of October 20, 2022), only two WPV1 cases were reported in two regions: one each from Paktika (Southeast Region) and Kunar provinces (East Region) (Table) (Figure 1) (Figure 2). All six patients in 2021 and 2022 were aged 10–25 months; three had never received OPV through RI services but had received 1 SIA dose, one had never received any OPV, one reportedly received 2 RI doses and 1 SIA dose, and one reportedly received 4 RI doses and 7 SIA doses.

Genomic sequence analysis of the region encoding the viral capsid protein 1 (VP1) of poliovirus isolates provided evidence of cross-border transmission between Afghanistan and Pakistan during 2019–2022, with sustained local transmission in both countries. During January 2021–September 2022, four of six WPV1 isolates from AFP patients and one of four WPV1 ES isolates from Afghanistan had their closest genetic links to WPV1 isolates from Pakistan. The poliovirus isolated from the first case during 2022, reported from Paktika province (Southeast Region), was genetically linked to previous circulation in Pakistan’s Baluchistan province. The poliovirus from the second 2022 case, reported from Kunar province (East Region), was genetically linked with transmission in the Northeast Region of Afghanistan. During January 2021–September 2022, only two WPV1 genetic clusters (groups of viruses sharing ≥95% VP1 sequence identity) were detected among AFP cases and environmental samples. Of the five WPV1 viruses detected in 2021, two (40%) were orphan viruses,^§§ indicating possible gaps in surveillance; no orphan viruses have been detected in 2022 to date.

Among 43 cVDPV2 cases reported in 2021, 29 (67%) were in the PAK-GB-1 emergence group, first detected in Gilgit-Baltistan, Pakistan, and 14 were in the AFG-NGR-1 emergence group, first detected in Afghanistan’s Nangarhar province (3). Paralysis onset in the patient with the most recently detected cVDPV2 case was in July 2021.

Discussion

After confirmation of large numbers of both WPV1 and cVDPV2 polio cases during 2019–2020 in Afghanistan and Pakistan, both countries jointly reported five WPV1 and 51 cVDPV2 cases in 2021 (1). Given that the latest cVDPV2 detection was in Pakistan in August 2021, transmission of cVDPV2 in both countries is likely interrupted. Resurgence of WPV1 cases occurred in 2022 in the south of Khyber Pakhtunkhwa province of Pakistan, an area that directly borders Afghanistan, with substantial social ties and population movement. As of October 20, 2022, Afghanistan has reported two WPV1 cases, one each in the East and Southeast regions. After the political transition, the de facto government’s public health authorities implemented an aggressive SIA schedule during November 2021–September 2022, which resulted in a substantial reduction in the number of unreached children. However, as of September 2022, >85% of children in the South Region where polio is endemic live in areas where restrictions on SIA implementation methods continue.

The findings in this report are subject to at least one limitation. The quality of data on SIA implementation is limited by the low accuracy of reported coverage data. The Global Polio Eradication Initiative is supporting the national program to establish a comprehensive data management system and providing ongoing staff member training.

Current polio eradication efforts in Afghanistan are challenged by a complex humanitarian emergency resulting from the combined impacts of a rapid government transition and a depressed economy, droughts, floods, food insecurity, displacement, and severe gaps in delivery of health services (7). In June 2022, a 5.9 magnitude earthquake struck Khost province in the Southeast Region, killing more than 1,000 persons and displacing entire communities (8). With progress broadening SIA access since the political transition, the opportunity to end WPV1 transmission in Afghanistan before the end of 2023 appears to be attainable. Ending transmission, however, depends on continued and expanded SIAs throughout the country, including in the high-risk provinces of the South Region.