We plan a parallel, single-blind multicentre RCT (with concealed allocation) to determine the efficacy of maternal PHiD-CV immunisation on infant respiratory outcomes. Our primary question is: Does vaccinating pregnant Indigenous women with PHiD-CV (compared to controls) reduce ALRI in their infants in the first year of life? Our primary hypothesis is that: Infants born to pregnant women who received PCV-HiD have at least 30% less ALRIs in their first year of life, compared to those who did not receive the vaccine.