Since the 1988 World Health Assembly resolution to eradicate polio globally the incidence of polio has been reduced dramatically In 2003, there were approximately 2000 reported cases worldwide and polio was endemic in only seven countries (Afghanistan, Egypt, India, Niger, Nigeria, Pakistan, and Somalia). As the achievement and certification of polio eradication draws near, WHO is evaluating potential post-certification immunization policies. At the beginning of the initiative, it was assumed that polio vaccination would simply be withdrawn after certification of polio eradication followed by the accrual of financial benefits resulting from ceasing vaccination. Over the past decade newly identified oral poliovirus vaccine (OPV) risks such as circulating vaccine-derived polioviruses (cVDPVs) and rare chronic excretors of poliovirus, containment concerns, and the perceived bioterrorism threat have led to a scientific and economic reassessment of potential post-certification immunization policies. Although countries will ultimately make their own immunization policy decisions after careful assessment of their own costs, risks, and benefits, it is likely that they (particularly developing countries) will be greatly influenced by global policies recommended by WHO.
We estimated the global costs associated with immunization policies currently being considered: continue OPV, OPV cessation with optional IPV, and universal inactivated poliovirus vaccine (IPV) (1). The costs of each policy are based on the total financial programme costs and the health costs, which we have limited to the number of cases of vaccine-associated paralytic poliomyelitis (VAPP). The global policy costs presented are meant as an aid for comparing the policies on a global scale. A comprehensive research agenda is being implemented to carefully assess the risks associated with these policies, but this is beyond the scope of our paper.
Methods and assumptions
This paper focuses on estimating the global costs of implementing each immunization policy, maintaining surveillance at current levels, and developing a vaccine stockpile. The costs of an outbreak were not included in this analysis (2). The costs of immunization were estimated by projecting vaccination coverage levels and the costs of the vaccine and its administration. We have included the number of projected VAPP cases under each policy scenario as a health cost and projected outbreak response capacity costs to include the current cost of maintaining epidemiological and laboratory surveillance and the cost of a vaccine stockpile. Vaccination coverage levels and labour costs vary for all countries. In addition, countries vary in their current polio immunization policies, and we have assumed that countries will make their own policy decision for each global policy recommendation. Policy assumptions for high-, middle-, and low-income countries were made on the basis of WHO projections on vaccine demand (H. Everts, C. Maher, personal communication, 2002). We categorized the country decisions by economic status using World Bank classifications (low income gross national income per capita (GNI), US$ 735 or lower; middle income GNI, US$ 736-9075; high income GNI, US$ 9,076 or higher) (3). For example, some high-income countries, such as the United States, have already switched to IPV to avoid the risk of VAPP associated with OPV. Therefore, we have assumed that by the time of certification, high-income countries will switch to IPV regardless of the global policy recommendation. We have assumed that middle-income countries will gradually switch to IPV after certification and low-income countries will follow the global policy recommendation. Countries with very low coverage (below 70%) and that are recently endemic with polio were assumed to provide routine OPV and periodic supplemental vaccination by conducting national immunization days (NIDs) until 2010. Costs were estimated for all countries according to income groupings. …