Methods: We conducted a historical cohort study of NT Indigenous infants born between 1st January 2006 and 31st December 2015 and followed until age 12 months. Data were from administrative hospital and perinatal datasets. International classification of diseases codes were used to identify respiratory hospitalisations of interest: all cause ALRI, all cause pneumonia, bacterial pneumonia, viral pneumonia, influenza-like illness (ILI), respiratory syncytial virus ALRI (RSV-ALRI) and pneumococcal ALRI. Incidence rates were compared between PCV eras (7-valent PCV-PCV7, 2006-2009; PCV10, 2009-2011; PCV13, 2011-2015) using interrupted time trend analysis and negative binomial regression.
Findings: Over the study period 4138 ALRI episodes (31% of all hospitalisations) occurred among 2888 of the 14594 infants (20% of the cohort). The overall ALRI hospitalisation rate was 29.7 episodes per 100 child-years. Prominent risk factors associated with ALRI hospitalisation were living in a remote community or the Central desert region, being born preterm or with low birth weight. ALRI rates were lowest in the PCV13 era in association with a significant reduction in bacterial pneumonia hospitalisations in the PCV13 relative to the PCV10 (IRR 0∙68, 95% CI 0∙57-0∙81) and PCV7 (IRR 0∙70, 95% CI 0∙60-0∙81) eras. In contrast, RSV-ALRI rates were 4∙9 episodes per 100 child-years in each era.
Interpretation: We found a 30% reduction in bacterial-coded pneumonia hospitalisation episodes during the era of PCV13 use. Despite this, one in five NT Indigenous infants continue to be hospitalised with an ALRI in their first year of life. RSV associated ALRI rates were high and remained unchanged over a decade.