In order to obtain the earliest possible protection against invasive pneumococcal disease, achieve optimal coverage and reduce burden of early carriage, neonatal pneumococcal conjugate vaccine (PCV) immunization needs to be considered. This study in the PNG highlands will enrol 312 infants at birth, who will be randomised to receive PCV either at 1-2-3 months (infant schedule according to PNG national EPI schedule) or 0-1-2 months of age (neonatal schedule) or receive only routine immunizations (controls). Blood samples will be taken at birth-2-3-4 months of age, pre- and post-pneumococcal polysaccharide booster (23vPPV) at 9-10 months of age (to assess immune memory) and at 18 months at study completion. Carriage will be assessed weekly for the first month of life and at regular intervals thereafter. There will be ongoing surveillance for respiratory and other diseases throughout the study. In addition to serotype-specific IgG, we will examine IgG avidity, IgG subclasses, mucosal IgA and T-cell cytokine responses to PCV and pneumococcal protein antigens. To ensure immunological safety, particularly for neonatal PCV, immune responses to concomitant vaccines and viral and environmental antigens will also be examined as well as overall T-cell maturation.