Sex-differential effects on mortality of BCG and diphtheria-tetanus-pertussis vaccines in a rural area with high vaccination coverage: observational study from Senegal.

BACKGROUND: Diphtheria-tetanus-pertussis (DTP) may be associated with increased female mortality; the effect of co-administration with BCG is not known.

METHODS: Between 1989 and 1997, we examined female and male mortality rates in rural Senegal where 7824 infants received the first dose of DTP and inactivated polio vaccine (DTP-IPV) with BCG. Subsequent doses of DTP-IPV were administered alone. We analysed mortality according to sex and number of doses of DTP-IPV vaccine.

RESULTS: BCG and DTP-IPV1 simultaneously reduced mortality from 60/1000 person-years in unvaccinated girls to 35/1000 person-years, but mortality increased with subsequent doses of DTP-IPV to 45/1000 person-years. Among boys, BCG and DTP-IPV1 simultaneously reduced mortality from 72/1000 person-years to 60/1000 person-years and mortality decreased further with subsequent doses of DTP-IPV to 34/1000 person-years. In age-adjusted analyses, female-male mortality rate ratios were 0.83(95% CI 0.50-1.40) among unvaccinated children and 0.58 (95% CI 0.35-0.96) among children vaccinated simultaneously with BCG and DTP-IPV1, but increased to 1.17 (95% CI 0.67-2.03) after DTP-IPV2, and 1.63 (95% CI 0.86-3.10) after DTP-IPV3. Difference in vaccination coverage could not explain these sex-differential patterns; girls had significantly better weight-for-age than boys so nutritional status did not explain the increase in female mortality after DTP-IPV3.

CONCLUSIONS: Whereas BCG co-administered with DTP-IPV was associated with lower female than male mortality, subsequent DTP-IPV vaccinations were associated with an increase in female mortality relative to male mortality.