Age-specific changes in the female–male mortality ratio related to the pattern of vaccinations: An observational study from rural Gambia

Abstract

Background According to studies from Guinea-Bissau and Senegal, live vaccines may reduce the female–male mortality ratio (MR) whereas inactivated vaccines increase this ratio. We used data from The Gambia to examine whether similar tendencies could be found in a different setting. Setting Forty villages in the Farafenni area in rural Gambia. Subjects A population of 17,000 was followed with demographic surveillance between 1998 and 2002; 537 children less than 5 years of age died in this period. Methods We used two vaccination surveys and community mortality data to examine, first, the female–male mortality ratio (MR) in the age groups in which DTP and MV are recommended and have a high coverage. Second, using vaccination cards seen post-mortem, we examined the distribution of live or inactivated vaccines as last vaccination in different age groups. Third, we examined the effect of DTP and MV administered simultaneously. Main outcome measures The female–male MR in different age groups and for different vaccines. Results Vaccination coverage was high for BCG, third dose of DTP (DTP3) and MV, reaching a level of 80–90% within a few months of the recommended age of vaccination. First, the female–male MR was 0.93 (0.63–1.38) in the first 2 months of life when children had received no vaccination or the combination of BCG, HBV and OPV. From 2 to 8 months of age, with DTP and HBV being the main vaccinations, the female–male MR was 1.28 (0.86–1.89). Between 9 and 17 months of age, with MV as the main vaccination, this ratio dropped to 0.73 (0.50–1.07), a significant inversion of the female–male MR ( p = 0.045). Second, using information from vaccination cards of dead children, boys who died at 2–4 months of age were more likely to have received live BCG and girls to have received inactivated DTP and HBV as last vaccination ( p < 0.001). At 5–8 months of age, essentially all dead children had received DTP as last vaccination and the female–male MR was 1.68 (0.96–2.93), whereas the MR was 0.70 (0.43–1.15) at 12–17 months of age when nearly all dead children had received MV ( p = 0.022). Third, compared with the general population of children who had received MV, dead children who had received MV were more likely to have received DTP3 simultaneously with MV (relative risk (RR) = 5.59 (2.10–14.8)) or after MV (RR = 2.61 (1.13–6.05)). Conclusion Most children dying at a specific age had received the recommended vaccines. BCG and MV as last vaccination was associated with a low female–male MR, whereas DTP as last vaccination was associated with a high female–male MR. These trends are consistent with observations from other African countries.