The PREV-IX_COMBO trial is a randomised controlled trial (RCT) of these two pneumococcal conjugate vaccines currently licensed in Australia. Participating Indigenous infants living in remote communities in 4 regions of the NT are randomised between 28 and 38 days of age and allocated to one of three groups: PHiD-CV10 at 2, 4, 6 months or PCV13 at 2,4,6 months, or an investigational group of a 4-dose combination schedule of PHiD-CV10 at 1,2, and 4 months plus PCV13 at 6 months.