The costs of scaling up vaccination in the world's poorest countries.

We examine the relationship between country-level average costs and coverage levels for diptheria-pertussis-tetanus (DTP) vaccines. Coverage data are from the World Health Organization, and cost data are from financial sustainability plans filed with the Global Alliance for Vaccines and Immunization (GAVI) by forty countries from 2000 to 2003. In this data set, average costs are lower for countries that vaccinate more children. At the highest numbers of covered children, there was no trend toward higher average costs. Vaccine programs in this set of poor countries have not yet scaled up to the point at which diminishing marginal returns are observed.