Paralleling the demographic transition is the epidemiologic transition, which traces the long-term mortality decline in terms of changes in the major killer diseases. Only in Stage 4 has modern clinical medicine made a significant difference to our life chances. Most of our gains spring from industrialization, and also from public health measures that include mass vaccination, insecticide spraying, and water purification. Stage 4 also shows us that while we may have curbed communicable disease, we are far from eradicating it, as emergent infections like HIV, Ebola and SARS, and re-emergent infections like tuberculosis, continually remind us.