Abstract
The US Agency for International Development (USAID) launched a significant effort to improve global immunization coverage in the mid-1980s, beginning a long history of investments in various approaches to supporting the improvement of national vaccination programs in developing countries. As Primary Health Care evolved, USAID's approach to immunization also evolved, heavily influenced by the child survival revolution, a period when the global community struggled to define an approach that incorporated the essence of the Alma-Ata Conference with the selective primary health-care approach. Eventually, what became known as the 'twin engines' approach, a focus on two high impact interventions-immunization and oral rehydration therapy-would characterize USAID's child survival program. As coverage fell during the less favorable international economic climate of the 1990s, USAID re-evaluated its approach and moved toward a more system strengthening concept. At the turn of the century, with the pressure of measurable impact, the Agency moved toward more easily measured inputs and away from the longer-term system strengthening activities of the previous two decades. This approach emphasized simple, proven technologies, more public/private partnerships and greater investment in vertical disease programs with short-term impact. Investments such as polio eradication and vaccine purchase through the GAVI Alliance (formerly the Global Alliance for Vaccines and Immunization) became funding priorities for the Agency. Today, USAID faces a challenge of how it will support developing country vaccination programs. Will it provide assistance through vertical disease efforts and material inputs or will it shift back to a more system strengthening approach? The answer has not yet been provided.