Effect of infant immunisation on childhood mortality in rural Bangladesh: analysis of health and demographic surveillance data

Summary

Background

In developing countries, immunisation programmes must compete with other strategies to improve public health and quality of life. Studies of long-term effects of immunisation programmes are rare. We assessed associations between vaccinations and mortality over 15 years after the introduction of routine infant immunisation programmes in Matlab, Bangladesh.

Methods

We analysed data recorded in a comprehensive health and demographic surveillance system from 1986 to 2001. We did univariate analyses and assessed vaccinations as independent factors with other variables in Cox models with time dependent covariates.

Findings

Diphtheria-tetanus-pertussis (DTP) and oral polio vaccination were independently associated with decreased risk of death before age 9 months, as were amount of maternal education, maternal age, and birth order of the child. DTP vaccination was associated with increased survival (hazard ratio=0·76, 95% CI 0·67–0·88; p=0·001) in a model evaluating mortality between 6 weeks and 9 months of age. Measles vaccination was also associated with increased survival when data after late immunisation with DTP and Bacille Calmette-Guérin (BCG) were excluded. BCG vaccination was associated with reduced survival; however, children vaccinated with BCG during the first 6 months of life had significantly lower risk of death than those vaccinated later (hazard ratio=0·59; 95% CI 0·47–0·73; p=0·0001).

Interpretation

By contrast with previous findings, we noted substantially reduced mortality among children who received DTP vaccine. This effect could be due to actual protection against pertussis disease and secondary illnesses or to a non-specific benefit, although we cannot rule out epidemiological artifact. Our findings show the value of population-based health surveillance systems.

Introduction

Immunisation prevents illness and death from many important infectious diseases. Rapid reductions in rates of vaccine-preventable diseases and associated mortality have followed introduction of new vaccines for routine use in infants.¹ However, as immunisation programmes mature, problems may arise. Enthusiasm for high vaccine coverage can be difficult to maintain in the face of falling disease rates and coincident focus on real or conjectured vaccine-associated adverse events.² In impoverished developing countries, where vaccine-preventable diseases are among many contributors to mortality in infants and children, it is challenging and increasingly important to demonstrate the effect and value of immunisation programmes, which must compete with other cost-effective interventions for extremely limited resources.3, 4 A report from Guinea-Bissau showed lower than expected mortality associated with Bacille Calmette-Guérin (BCG) and measles vaccines, and increased mortality after diphtheria-tetanus-pertussis (DTP) and oral poliovirus vaccine (OPV) vaccinations.⁵ These unexpected observations need to be further studied.⁶ We used data from a comprehensive health and demographic surveillance system in Matlab to assess whether immunisations have an effect on mortality among Bangladeshi children in a mostly rural setting.