Non-specific beneficial effect of measles immunisation: analysis of mortality studies from developing countries

Abstract

Objective: To examine whether the reduction in mortality after standard titre measles immunisation in developing countries can be explained simply by the prevention of acute measles and its long term consequences.

Design: An analysis of all studies comparing mortality of unimmunised children and children immunised with standard titre measles vaccine in developing countries.

Studies: 10 cohort and two case-control studies from Bangladesh, Benin, Burundi, Guinea-Bissau, Haiti, Senegal, and Zaire.

Main outcome measures: Protective efficacy of standard titre measles immunisation against all cause mortality. Extent to which difference in mortality between immunised and unimmunised children could be explained by prevention of measles disease.

Results: Protective efficacy against death after measles immunisation ranged from 30% to 86%. Efficacy was highest in the studies with short follow up and when 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 cases of measles were excluded from the analysis. Diphtheria-tetanus-pertussis and polio vaccinations were not associated with reduction in mortality.

Conclusion: These observations suggest that standard titre measles vaccine may confer a beneficial effect which is unrelated to the specific protection against measles disease.

PIP: Ten cohort and two case-control studies from Bangladesh, Benin, Burundi, Guinea-Bissau, Haiti, Senegal, and Zaire comparing the mortality of nonimmunized children and children immunized with standard titre measles vaccine were analyzed to determine whether the reduction in mortality after standard titre measles immunization can be explained simply by the prevention of acute measles and its long-term consequences. Protective efficacy against death after measles immunization ranged from 30% to 86%. Efficacy was highest in the studies with short follow-up and when children were immunized in infancy. 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 cases of measles were excluded from the analysis. Finally, diphtheria-tetanus-pertussis and polio vaccinations were not associated with reduction in mortality. These findings suggest that standard titre measles vaccine may confer a beneficial effect against mortality which is unrelated to the specific protection against measles disease.