Lessons for the past: Third World evidence and the reinterpretation of developed world mortality declines

Measles is the largest single killing infection of children in the world, and it is likely that its toll is heightened by the occurrence of a serious delayed effect of early infection. Variations in measles mortality, and in the seriousness of infection, have often been explained in terms of nutritional factors, but intercountry comparisons within the Third World fail to bear this out. In this paper an alternative interpretation is developed, based on the severity of the infective dose to which individuals are exposed. It is shown that this can account for a wide variety of observations which are inexplicable on the nutritional hypothesis, and can also explain the severity of virginsoil epidemics without reference to the effects of genetic selection. The exposure hypothesis predicts that measles vaccination should have a marked effect on childhood mortality as a whole, and this prediction is born out in practice. The success of this interpretation has important implications for our understanding of historical mortality declines in the developed countries, particularly the decline in smallpox mortality.