We thus propose to study, in a randomised controlled trial of measles vaccination taking place in Guinea-Bissau, the immunology of non-specific effects of vaccination, and their interaction with sex. Specifically, among children who have received the 3 recommended doses of DTP, we will be able to compare the cytokine and antibody profiles of children who receive an early dose of measles vaccine at 4½ months of age with children who receive no additional vaccine at this age.