Seroprevalence of Anti-polio Antibodies in Children from Polio High-risk Areas of Pakistan: A Cross-Sectional Survey 2015-2016

Background: Pakistan is one of the 3 remaining wild poliovirus endemic countries. We collected sera from children to assess the prevalence of poliovirus antibodies in selected high-risk areas for poliovirus transmission. Methods: Children in 2 age groups (6-11 and 36-48 months) were randomly selected between November 2015 and March 2016 in 6 areas of Pakistan (Sindh Province: Karachi and Kashmore; Khyber Pakhtunkhwa Province: Peshawar, Bannu and Nowshera; Punjab Province: Faisalabad). After obtaining informed consent, basic demographic and vaccination history data were collected, 1 peripheral venipuncture was obtained, and assays to detect poliovirus (PV)-neutralizing antibodies were performed. Results: A total of 1301 children were enrolled and had peripheral blood drawn that analyzed. Study subjects were evenly distributed among survey sites and age groups. Anti-polio seroprevalence differed significantly among geographic areas (P < 0.001); in the 6-11 months group, it ranged between 89% and 98%, 58% and 95%, and 74% and 96% for PV serotypes 1, 2 and 3, respectively; in 36-48 months group, it ranged between 99% and 100%, 95% and 100%, and 92% and 100% for PV 1, 2, and 3, respectively. Having received inactivate poliovirus vaccine, malnourishment (stunting) and educational level of parents were found to be associated with presence of anti-polio antibodies. Conclusion: The polio eradication program achieved overall high serologic protection; however, immunity gaps in young children in the high polio risk areas remain. These gaps enable sustained circulation of wild poliovirus type 1, and pose risk for emergence of vaccine-derived polioviruses. Focusing on the lowest socioeconomic strata of society, where malnutrition is most prevalent, could accelerate poliovirus eradication.