When the Global Polio Eradication Initiative (GPEI) began in 1988, wild poliovirus (WPV) was being transmitted in 125 countries; currently, transmission of WPV type 1 (WPV1) continues in only 2 countries, Afghanistan and Pakistan. (1, 2) This report describes Pakistan's progress towards 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 25 August 2021, Pakistan had reported only 1 case of WPV1. Circulating vaccine-derived poliovirus (cVDPV) has emerged as a result of regained neurovirulence of attenuated oral poliovirus vaccine (OPV) virus after prolonged circulation in under-immunized populations; this can lead to paralysis. In Pakistan, 22 cases of cVDPV type 2 (cVDPV2) were reported in 2019, 135 cases were reported in 2020 and 8 cases have been reported in 2021 to date. Because of the COVID-19 pandemic, planned supplementary immunization activities (SIAs) (5) were suspended during mid-March-June 2020; (3,6) however, 7 SIAs were implemented during July 2020-July 2021 with no substantial decrease in SIA quality. Improving the quality of polio SIAs, vaccinating immigrants from Afghanistan and implementing changes to enhance programme accountability and performance would help the Pakistan polio programme to achieve its goal of interrupting WPV1 transmission by the end of 2022.
Essential (routine) immunization: For 2020, WHO and UNICEF estimated Pakistan's national coverage with 3 doses of OPV at 83% and with 1 dose of inactivated poliovirus vaccine by age 12 months at 85%, respectively. (7) A 2021 WHO and Gavi, the Vaccine Alliance-sponsored survey indicated that the proportion of children aged 12-23 months who were fully immunized, by province, ranged from 37.5% in Balochistan to 88.9% in Punjab. None of the districts in the provinces of Balochistan, Khyber Pakhtunkhwa and Sindh achieved [greater than or equal to]80% coverage among children aged 12-23 months, including the core WPV1 reservoir districts in these provinces, namely Quetta (45.5% coverage), Peshawar (76.6%) and Karachi (63.9%), while 31 of 36 (86%) districts in Punjab province achieved [greater than or equal to]80% coverage.
Supplementary immunization activities: Pakistan was among 155 OPV-using countries that ceased all use of OPV type 2 in 2016; the standard product for outbreak response to confirmed cVDPV2 outbreaks is now monovalent OPV type 2 (mOPV2, containing Sabinstrain type 2). (8) GPEI authorized restarting the filling of stocks of trivalent OPV (tOPV, containing Sabin-strain types 1, 2 and 3) for use in SIAs where there is co-circulation of WPV1 and cVDPV2, for efficiency in scheduling and implementation. During 2020, 4 national immunization days (NIDs) and 2 subnational immunization days (SNIDs) targeting children aged <5 years were conducted with bivalent OPV (bOPV; containing Sabin strain types 1 and 3) and, in areas with cVDPV2 transmission, either mOPV2 or tOPV. SIAs were suspended during March-June 2020 due to control measures for the COVID-19 pandemic, including procurement of personal protective equipment for vaccination teams. SIAs resumed in July 2020 with a small-scale mOPV2 case-response vaccination campaign, followed by a broader mOPV2 SNID in August, a tOPV...