The global vaccination gap.

Abstract

V accination can change the ecology of infectious disease in human populations. It converts the equation of transmissibility in susceptible populations to predictable calculations of the length of time that an infectious agent may survive in immunized communities. But the potential eradication or control of many infectious diseases is threatened by a staggering disparity in vaccination efforts worldwide. The successes of the 20th-century global immunization programs have been significant: the eradication of smallpox and the elimination of poliomyelitis in Europe, the Americas, and much of Asia. Yet a huge gap exists between the industrialized world and sub-Saharan Africa in the immunization rates for diphtheria, tetanus, and pertussis (DTP), the most accessible and affordable childhood vaccine. The DTP vaccination rate on the African continent has hovered around 50% for the past 15 years, with approximately one-quarter of the countries in the region falling below this average. The persistence of this gap is an outcome of unsustained immunization efforts along with a deteriorating infrastructure and lack of political will. Furthermore, immunization rates of other vaccines, such as that for hepatitis B, are far below that for DTP. The recently reported and potentially explosive recurrence of poliomyelitis in Africa is a wake-up call. The sad result is an estimated 2 to 3 million childhood deaths each year in the developing world that could have been prevented. Looking ahead, worldwide planning has barely begun for a new generation of vaccines to prevent infections that cause other major killers such as pneumonia and diarrhea. ![Figure][1] CREDIT: WHO Although the global community is responding to worldwide needs with vaccine initiatives and funds, success cannot be realized until there is agreement on, and commitment to, the prerequisites for successful immunization programs at national levels. For a vaccine to reduce the transmission of an infectious agent and subsequently its burden of illness, a majority of susceptible individuals have to become resistant to the agent of disease. It was estimated that for smallpox eradication, immunization of 70 to 80% of the population was necessary. In contrast, measles immunization needs to achieve coverage rates of 90 to 95%. These rates apply equally to developed and developing countries, as demonstrated by the recent resurgence over the past decade of measles in England and Japan, as vaccination rates fell below a critical level. Another determinant of vaccination program success is the sustainability of community-based immunization efforts. In practical terms, these programs aim to annually convert a proportion of the birth cohort into a resistant population. Such annual immunization programs need approximately two decades of continuous application to reach their full impact. The outcome of immunization programs that do not meet both of these criteria is at best marginal. Leadership and government commitment to closing the global vaccination gap have to come from the affected countries. It is the only way to make a credible case for help from the developed world. The seriousness of the task has to be matched with the magnitude of local investment in health. Governments of these countries must place disease prevention above political conflict or weapons purchase. Strong leaders are needed to mobilize local communities and entire nations for the administration of vaccines, as was the case in Central and South America, where “Immunization Days” or “Immunization Weeks” resulted in the eradication of paralytic poliomyelitis. Clear demonstrations of societal will and leadership for change are not evident today in affected countries; they are glaringly absent. Certainly, closing the gap will require national and multinational resources and efforts. It is estimated by the Global Alliance for Vaccines and Immunization that expanding the immunization program of the World Health Organization, as well as beginning the systematic introduction of newer vaccines, will require billions of dollars in funding over two decades. It is also sobering that global vaccination efforts, which are the most effective disease prevention strategy available today, are so disjointed. The absence of national leadership is painfully obvious, and unless governments and organizations at the highest levels commit to a common and coordinated immunization plan, the world will continue to be overwhelmed by unnecessary death. [1]: pending:yes