Factors associated with immunisation coverage and timeliness in New Zealand.

Background: Immunisation coverage in New Zealand is lower than what is necessary to prevent large epidemics of pertussis. Primary care is where most immunisation delivery occurs. General practices vary in their structure and organisation, both in a general sense and specifically with respect to immunisation delivery.
Aim: To identify the structural and organisational characteristics of general practices associated with higher immunisation coverage and more timely immunisation delivery.
Design of Study: A random sample of practices during 2005 and 2006.
Setting: General practices in the Auckland and Midland regions, with over-sampling of indigenous Maori governance practices.
Method: Practice immunisation coverage and timeliness were measured. Primary care practice characteristics relevant to immunisation delivery by the practice were described. Associations of these practice characteristics with higher practice immunisation coverage and more timely immunisation delivery were determined.
Results: A total of 124 (61%) of 205 eligible practices were recruited. A median (25th to 75th centile) of 71% (57-77%) of registered children at each practice were fully immunised, and 56% (40-64%) had no immunisation delay. In multivariate analyses, both practice immunisation coverage (P<0.001) and timeliness (P<0.001) decreased with increased social deprivation. After adjustment for socioeconomic deprivation, region, and governance, immunisation coverage and timeliness were better at practices that enrolled children at a younger age (coverage: P = 0.002; timeliness P = 0.007), used one of the four available practice management systems (coverage: P<0.001; timeliness: P = 0.006), and had no staff shortages (coverage: P = 0.027; timeliness: P = 0.021).
Conclusion: Practice immunisation coverage and timeliness vary widely in New Zealand. General organisational and structural aspects of general practices are key determinants of general practice immunisation delivery.