Hill DL, Carr EJ, Rutishauser T, et al. - Experts intended to distinguish factors that shape immune development in children under 5 years of age from Tanzania and Mozambique by detailed immunophenotyping of longitudinal blood samples collected during the RTS,S malaria vaccine phase 3 trial. In these cohorts, during the first years of life, the composition of the immune system is dynamically transformed, and this was further affected by geographical location, with some immune cell types giving an altered rate of development in Tanzanian children matched to Dutch children enrolled in the Generation R population-based cohort study. At the time of vaccination, high-titer antibody responses to the RTS,S/AS01E vaccine were correlated with an activated immune profile, including an improved frequency of antibody-secreting plasmablasts and follicular helper T cells. The data indicated that in children, the composition of the immune system varies according to age, geographical location, and anemia status.