Investigating spatial variation and change (2006-2017) in childhood immunisation coverage in New Zealand

Background: Immunisation is a safe and effective way of protecting children and adults against harmful diseases. However, immunisation coverage of children is declining in some parts of New Zealand. Aim: Use a nationwide sample to first, examine the socioeconomic and demographic determinants of immunisation coverage and spatial variation in these determinants. Second, it investigates change in immunisation coverage in New Zealand over time. Methods: Individual immunisation records were obtained from the National Immunisation Register (NIR) (2005-2017; 4,482,499 events). We calculated the average immunisation coverage by year and milestone age for census area units (CAU) and then examined the immunisation coverage by selected socioeconomic and demographic determinants. Finally, local variations in the association between immunisation coverage and selected determinants were investigated using geographically weighted regression. Results: Findings showed a decrease of immunisation rates in recent years in CAUs with high immunisation coverage in the least deprived areas and increasing immunisation rates in more deprived areas. Nearly all explanatory variables exhibited a spatial variation in their association with immunisation coverage. For instance, the strongest negative effect of area-level deprivation is observed in the northern part of the South Island, the central-southern part of the North Island, around Auckland, and in Northland. Conclusion: Our findings show that childhood immunisation coverage varies by socioeconomic and demographic factors across CAUs. We also identify important spatial variation and changes over time in recent years. This evidence can be used to improve immunisation related policy in New Zealand.