A non-specific, beneficial effect of measles vaccination. Analysis of mortality studies from developing countries

The study examined whether the reduction in mortality after standard titre measles immunization in developing countries can be explained by the prevention of acute measles and its long-term consequences. All studies comparing mortality of unimmunised children and children immunised with standard titre measles vaccine in developing countries were included; ten cohort and two case-control studies from Bangladesh, Benin, Burundi, Guinea-Bissau, Haiti, Senegal, and Zaire. We examined the protective efficacy of standard titre measles immunization against all cause mortality. Furthermore, by restricting the analysis to children who had not developed measles, we examined how much of the difference in mortality between immunised and unimmunised children could be explained by prevention of measles disease. In the ten cohort studies, protective efficacy against death after measles immunization was found to be in the range of 30-86%. Efficacy was highest in the studies with short follow-up and where children were immunised in infancy (range: 44-100%). Vaccine efficacy against death was much greater than the proportion of deaths attributed to acute measles disease. In four studies from Guinea-Bissau, Senegal and Burundi, vaccine efficacy against death remained almost unchanged when measles cases were excluded from the analysis. Hence, the reduction in mortality among immunized children cannot be explained by the prevention of acute and long-term consequences of measles. In contrast to the effect of measles vaccine, studies from Guinea-Bissau, Senegal and Benin suggest that diphtheria-tetanus-pertussis and polio vaccinations are not associated with reduction in mortality. These observations suggest that standard titre measles vaccine may confer a beneficial effect which is unrelated to the specific protection against measles disease.