International Journal of Epidemiology, Volume 33, Number 2, pp. 374-380
IJE vol.33 no.2 © International Epidemiological Association 2004; all rights reserved.
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The introduction of diphtheria-tetanus-pertussis vaccine and child mortality in rural Guinea-Bissau: an observational study
Bandim Health Project, Apartado 861, Bissau, Guinea-Bissau; and Danish Epidemiology Science Centre, Statens Serum Institut, Copenhagen, Denmark
Correspondence: P Aaby, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S, Denmark. E-mail: psb{at}mail.gtelecom.gw
Background and objective Previous studies from areas with high mortality in West Africa have not found diphtheria-tetanus-pertussis (DTP) vaccine to be associated with the expected reduction in mortality, a few studies suggesting increased mortality. We therefore examined mortality when DTP was first introduced in rural areas of Guinea-Bissau in 1984–1987.
Setting Twenty villages in four regions have been followed with bi-annual examinations since 1979.
Subjects In all, 1657 children aged 2–8 months.
Design Children were weighed when attending the bi-annual examinations and they were vaccinated whenever vaccines were available. DTP was introduced in the beginning of 1984, oral polio vaccine later that year. We examined mortality for children aged 2–8 months who had received DTP and compared them with children who had not been vaccinated because they were absent, vaccines were not available, or they were sick.
Main outcome measure Mortality over the next 6 months from the day of examination for vaccinated and unvaccinated children.
Results Prior to the introduction of vaccines, children who were absent at a village examination had the same mortality as children who were present. During 1984–1987, children receiving DTP at 2–8 months of age had higher mortality over the next 6 months, the mortality rate ratio (MR) being 1.92 (95% CI: 1.04, 3.52) compared with DTP-unvaccinated children, adjusting for age, sex, season, period, BCG, and region. The MR was 1.81 (95% CI: 0.95, 3.45) for the first dose of DTP and 4.36 (95% CI: 1.28, 14.9) for the second and third dose. BCG was associated with slightly lower mortality (MR = 0.63, 95% CI: 0.30, 1.33), the MR for DTP and BCG being significantly inversed. Following subsequent visits and further vaccinations with DTP and measles vaccine, there was no difference in vaccination coverage and subsequent mortality between the DTP-vaccinated group and the initially DTP-unvaccinated group (MR = 1.06, 95% CI: 0.78, 1.44).
Conclusions In low-income countries with high mortality, DTP as the last vaccine received may be associated with slightly increased mortality. Since the pattern was inversed for BCG, the effect is unlikely to be due to higher-risk children having received vaccination. The role of DTP in high mortality areas needs to be clarified.
Keywords BCG, child mortality, DTP, gender differences, non-specific effects of vaccination
Accepted 8 July 2003
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