Determinants of immunization in polio super high-risk union councils of Pakistan.

BACKGROUND: The current polio epidemiology in Pakistan poses a unique challenge for global eradication as the country is affected by ongoing endemic poliovirus transmission. Across the country, 40 union councils (UCs) which serve as core reservoirs for poliovirus with continuous incidences of polio cases are categorized as super-high-risk union councils (SHRUCs). METHODOLOGY: A cross-sectional survey was conducted in 39 SHRUCs using a two-stage stratified cluster sampling technique. 6,976 children aged 12-23 months were covered. A structured questionnaire was used for data collection. Data were analyzed using STATA version 17. RESULTS: Based on both vaccination records and recall, 48.3% of children were fully-, 35.4 % were partially-, and 16.3% were non-vaccinated in the SHRUC districts. A child is considered fully vaccinated when h/she completed vaccination for BCG, OPV0, OPV 1-3, Penta 1-3, PCV 1-3, IPV, and MCV1. Vaccination cards were seen for over half of the children in the SHRUC districts of Khyber Pakhtunkhwa (KP) and the majority of the SHRUC districts in Sindh, except for the SHRUC district of Malir the districts of Balochistan. Results for polio vacancies show that 60.9% of children from the SHRUC districts were vaccinated with at least three doses of OPV and one dose of IPV, while 20.4% were vaccinated with any OPV doses or IPV and 18.7% of children did not receive any polio vaccines. The dropout rate between vaccine visits was higher than the WHO-recommended cutoff point of 10% for all vaccine doses in the SHRUC districts. The likelihood of being fully vaccinated was higher among the children of educated parents. Full vaccination was found significant among the children of any SHRUC districts compared to district Killa Abdullah. CONCLUSION: Context-specific strategies with more focus on community engagement and targeted mobilization, along with robust monitoring mechanisms, would help address the underlying challenges of under-immunization in the SHRUCs.

Preventing erosion of oral polio vaccine acceptance: A role for vaccinator visits and social norms.

BACKGROUND: With continued challenges to the timeline for polio transmission interruption in Pakistan, including COVID-19, there is a risk of oral polio vaccine campaign fatigue among caregivers of young children. Renewed efforts to minimize oral polio vaccine acceptance erosion may be needed. This study examines the possible role of social norms in protecting against acceptance erosion and the role of vaccinators in promoting these social norms. METHODS: Data were analyzed from a poll conducted by local interview teams between February 23 and April 5, 2016, among 4,070 parents and other caregivers of children under age 5 living in areas at high-risk for polio transmission in Pakistan. The sample was drawn via a stratified multistage cluster design utilizing random route methods at the household level. We calculated the prevalence of subjective and descriptive social norms around vaccine acceptance; vaccine acceptance and commitment to vaccinate in future; and experiences and views of polio vaccinators across the population. We examined the relationship between these social norms and vaccination behaviors as well as the relationship between experiences with and views of vaccinators and social norms using uncontrolled comparisons (t-tests of proportion) and logistic repressions to control for demographics. RESULTS: Both descriptive and subjective positive social norms were associated with vaccine acceptance and future commitment. Positive experiences with and views of vaccinators (trust, perceived technical knowledge, compassion, and overall pleasantness of the interaction) were associated with both descriptive and subjective positive social norms. CONCLUSIONS: These data support the idea that positive social norms could be protective against erosion of oral polio vaccine acceptance and that positive experiences with, and views of, vaccinators could help promote these positive social norms. Creative community engagement efforts may be able to leverage positive experiences with vaccinators to help foster social norms and protect against the risk of acceptance erosion.

Immunity and field efficacy of type 2-containing polio vaccines after cessation of trivalent oral polio vaccine: A population-based serological study in Pakistan.

BACKGROUND: In Pakistan and other countries using oral polio vaccine (OPV), immunity to type 2 poliovirus is now maintained by a single dose of inactivated polio vaccine (IPV) in routine immunization, supplemented in outbreak settings by monovalent OPV type 2 (mOPV2) and IPV. While well-studied in clinical trials, population protection against poliovirus type 2 achieved in routine and outbreak settings is generally unknown. METHODS: We conducted two phases of a population-based serological survey of 7940 children aged 6-11 months old, between November 2016 and October 2017 from 13 polio high-risk locations in Pakistan. RESULTS: Type 2 seroprevalence was 50% among children born after trivalent OPV (tOPV) withdrawal (April 2016), with heterogeneity across survey areas. Supplementary immunization activities (SIAs) with mOPV2 followed by IPV improved population immunity, varying from 89% in Pishin to 64% in Killa Abdullah, with little observed marginal benefit of subsequent campaigns. In the other high-risk districts surveyed, a single SIA with IPV was conducted and appeared to improve immunity to 57% in Karachi to 84% in Khyber. CONCLUSIONS: Our study documents declining population immunity following trivalent OPV withdrawal in Pakistan, and wide heterogeneity in the population impact of supplementary immunization campaigns. Differences between areas, attributable to vaccination campaign coverage, were far more important for type 2 humoral immunity than the number of vaccination campaigns or vaccines used. This emphasizes the importance of immunization campaign coverage for type 2 outbreak response in the final stages of polio eradication. Given the declining type 2 immunity in new birth cohorts it is also recommended that 2 or more doses of IPV should be introduced in the routine immunization program of Pakistan.