Pakistan is one of only three endemic countries in the world still struggling to interrupt poliovirus transmission and meet the target of global polio eradication by 2012. Polio supplementary immunization activities (SIAs) for the home delivery of oral polio vaccine (OPV) were initiated in the country in 2000, when 119 cases of polio were reported. Although the number of cases declined to 32 in 2007, it has been rising steadily since 2008. (1) In 2011 Pakistan reported the world's highest number of polio cases and some fear the country may become the last remaining host of polio on earth. The situation clearly poses a serious threat to the Global Polio Eradication Initiative (GPEI). (2-4) In Pakistan, elimination efforts have largely relied on a robust case detection system based on surveillance of acute flaccid paralysis cases and on mass door-to-door polio SIAs, of which more than 100 have been conducted since the year 2000. (5,6) Every child less than 5 years of age who resides in Pakistan has to be reached during each SIA, since multiple doses of OPV are needed in countries with high endemicity for children to develop adequate immunity against polio. (1-4) SIAs can vary in frequency but are usually held one to two months apart.
SIAs against polio are primarily organized by government officials with support from United Nations partners, mainly the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF). SIAs are intended to complement, not replace, routine immunization against polio. They aim to interrupt poliovirus circulation through administration of the oral polio vaccine (OPV) to every child aged <5 years in every vaccine SIA campaign, irrespective of immunization history. (7) Public announcements through media coverage, posters and banners are used to create awareness about upcoming polio SIAs and encourage participation. Social marketing and community mobilization efforts are organized by UNICEF, and the staff of WHO's Polio Eradication Initiative assist local health officials in organizing, implementing and monitoring SIAs. A large cadre of vaccinators, health workers and community volunteers administer OPV to eligible children through visits to all households and at fixed health facilities. (7,8)
Although high coverage (>90%) during polio SIAs has been reported in Pakistan, actual coverage is questionable. An official report of the Independent Monitoring Board of the Global Polio Eradication Initiative published in February 2012 highlighted major planning and execution gaps for polio SIAs in Pakistan. (3) Several factors have made the goal of eliminating polio in Pakistan elusive. These include inconsistent quality of SIAs; failure to immunize children in many areas; inaccessibility of children due to ongoing military conflict; massive floods; poor routine immunization services; a structurally weak polio eradication programme; large nomadic and internally-displaced populations, and the refusal of some parents to have their children vaccinated. (9,10) Many of these factors have led to the clustering of unimmunized children, who are at high risk of getting polio. (11)
Very few studies evaluating the results of polio SIAs in Karachi have been published. We chose Karachi for our study because polio is endemic in the city and the risk of transmission is among the highest in Pakistan. Karachi is, in fact, the only megacity in the world that has not yet succeeded in interrupting polio transmission. Besides, its population represents all ethnic groups in Pakistan. Given Karachi's large cultural and ethnic diversity, we studied a large representative sample of individuals living across the city, our objective being to assess parents' knowledge about polio, rates of non-participation in polio SIAs and reasons for non-participation. We ensured adequate representation of the Pashtun community, a group that comprises an estimated 35-40% of Karachi's population and yet has suffered 90% of recent polio cases in the city. …