Gender-specific mortality in DTP-IPV- and MMR ± MenC-eligible age groups to determine possible sex-differential effects of vaccination: an observational study

BACKGROUND Several studies suggested that vaccines could have non-specific effects on mortality depending on the type of vaccine. Non-specific effects seem to be different in boys and girls. In this study we want to investigate whether there are differences in gender-specific mortality among Dutch children according to the last vaccination received. We tested the hypothesis that the mortality rate ratio for girls versus boys is more favourable for girls following MMR±MenC vaccination (from 14 months of age) compared with the ratio following DTP-IPV vaccination (2-13 months of age). Secondarily, we investigated whether there were gender-specific changes in mortality following booster vaccination at 4 years of age. METHODS This observational study included all Dutch children aged 0-11 years from 2000 until 2011. Age groups were classified according to the last vaccination offered. The mortality rates for all natural causes of death were calculated by gender and age group. Incidence rate ratios (IRRs) were computed using a multivariable Poisson analysis to compare mortality in boys and girls across different age groups. RESULTS The study population consisted of 6,261,472 children. During the study period, 14,038 children (0.22%) died, 91% of which were attributed to a known natural cause of death. The mortality rate for natural causes was higher among boys than girls in all age groups. Adjusted IRRs for girls compared with boys ranged between 0.81 (95% CI 0.74-0.89) and 0.91 (95% CI 0.77-1.07) over the age groups. The IRR did not significantly differ between all vaccine-related age groups (p=0.723), between children 2-13 months (following DTP-IPV vaccination) and 14 months-3 years (following MMR±MenC vaccination) (p=0.493) and between children 14 months-3 years and 4-8 years old (following DTP-IPV vaccination) (p=0.868). CONCLUSIONS In the Netherlands, a high income country, no differences in gender-specific mortality related to the type of last vaccination received were observed in DTP-IPV- and MMR ± MenC eligible age groups. The inability to detect this effect indicates that when non-specific effects were present the effects were not reflected in changes in the differences in mortality between boys and girls. The findings in this large population-based study are reassuring for the continued trust in the safety of the national vaccination programme.