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MEDIA CENTER Measles Vaccination Shown to Improve Survival Chances of Poorest Children NEW YORK (12 July 2001) — By saving poor children from death due to measles or measles-related complications, vaccination programs appear to boost the long-term health prospects for poor children, who typically lag behind their economically advantaged peers. Researchers studying the role of child immunization in contributing to greater health care equity determined that unvaccinated children from very poor families face more than a threefold higher risk of subsequent early childhood death than vaccinated children from families of high economic status. While measles vaccination has little impact on mortality risks among children of higher economic status, the improvement in survival among children from poorer households is pronounced. The study, which analyzed longitudinal data from the International Centre for Diarrhoeal Disease Research (ICDDR,B) in Matlab, Bangladesh, appears in the June issue of Population and Development Review, a peer-reviewed journal published by the Population Council. Researchers Michael A. Koenig, David Bishai, and Mehrab Ali Khan examined whether preventive health technologies like vaccinations can improve the long-term survival prospects for the most vulnerable children. In the present study, female children and children from poorer families were considered especially vulnerable. Since 1966, the research center in Matlab has maintained a system of continuous surveillance of vital events in the area. In March 1982, measles vaccination was offered for all children aged nine months and older in two of the four blocks of the Matlab intervention area. Koenig and his colleagues analyzed the data from 16,270 vaccinated children and randomly matched controls to determine whether the measles vaccination contributed to long-term survival of vulnerable children. Initial work on the issue of health equity posited that socioeconomic and cultural factors were likely to diminish the impact of preventive or curative health technologies on improvements in survival. Under this theory, children "saved" from death by one intervention were likely to continue to be at high risk of illness and death from other causes, with the result that longer-term improvements in child survival associated with a specific intervention might be negligible. Subsequent refinement of the child survival framework introduced the concept of frailty, whereby a specific childhood disease may contribute to death not only directly, but indirectly as well, by producing more frail "survivors" who are at higher risk of dying from subsequent illness. Analyzing data from the Matlab population, Koenig and colleagues demonstrate that it is the most vulnerable children who largely benefit from interventions such as measles vaccination. "An unvaccinated child from a poor family faces more than a threefold higher risk of subsequent early child mortality compared to a vaccinated child from a family of high economic status," the authors maintain. "Our analysis has shown that the provision of measles vaccination alone has the potential to reduce these risks markedly—from over threefold to just over 1.5 times higher, a remarkable narrowing of differential mortality risk." According to the authors, the biomedical explanation of how measles vaccination disproportionately benefits vulnerable children remains unknown, and understanding of the specific mechanisms remains limited. "It has been hypothesized, for example, that measles vaccination may stimulate the immune system in nonspecific ways," they note. "Measles is known to be a devastating illness among children with poor nutritional reserves and can lead to a prolonged vulnerability to infectious illness and frailty, until visceral protein and vitamin A stores are replenished. Unresolved questions also remain as to whether the health equity effects reported here are confined to measles vaccination or extend to other child survival interventions as well." As of 1998, there were at least ten countries where measles vaccination reached less than 50 percent of eligible children, and over 25 countries where coverage was less than 80 percent, despite its relatively low cost of under US$0.50 per dose. As the authors note, unvaccinated children are not evenly distributed throughout the population, but are concentrated in families of lower socioeconomic status, precisely the children who would benefit most from child survival interventions such as measles vaccination. "The results of this study underscore the need for developing special strategies and targeted approaches for reaching the most disadvantaged children," they conclude. Michael A. Koenig is Associate Professor and David Bishai is Assistant Professor, Department of Population and Family Health Sciences, School of Hygiene and Public Health, the Johns Hopkins University. Mehrab Ali Khan is Assistant Scientist, ICDDR,B: Centre for Health and Population Research, Bangladesh. Population and Development Review, Vol. 27, No. 2, June 2001, also includes Notes and Commentary, Data and Perspectives, Archives, Book Reviews, and Documents. For subscription information call 212/339-0514, fax 212/755-6052, or email publications@popcouncil.org.
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