Evaluation of non-specific effects of infant immunizations on early infant mortality in a southern Indian population

OBJECTIVE: The aim of this study was to assess the relationship between receipt of routine childhood immunizations and infant mortality before 6 months of age. METHODS: This was an observational study of 10 274 infants, in a randomized trial of vitamin A supplementation, who received the study dose and survived to at least 1 week of age. The primary outcome was mortality before 6 months of age, analysed in Cox regression models as a function of vaccine receipt and gender. RESULTS: Receipt of Bacille Calmette Guerin (BCG) or diphtheria, tetanus, polio (DTP) vaccine was associated with significant reductions of one-half to two-thirds of mortality hazards; among girls, those who received both BCG and DTP experienced higher mortality than those who received only one of the two vaccines (hazards ratio 2.4; 95% confidence interval 1.2-5.0). CONCLUSION: The reduced mortality rate associated with receipt of BCG or DTP may be due to both biological and selection factors; the analyses regarding the combined effect of these vaccines and gender need to be replicated in other settings.