Factors associated with delayed infant immunization in a nationally representative cohort study

Background Many children in developed countries do not receive recommended vaccines on time. However, knowledge about factors related to timeliness remains limited. Quantifying the relative impact of parental attitudes compared with socio‐demographic factors for delayed immunization would inform policy responses. Methods Participants in the nationally representative Longitudinal Study of Australian Children were matched with their vaccination histories in the Australian Childhood Immunisation Register (N = 4,121). Information about the children and their families were collected in face‐to‐face interviews in 2003–2004. We considered whether children had completed the primary course for each recommended antigen due by 6 months old. Children were categorized as either fully immunized, delayed, or totally non‐immunized. The outcome was examined using logistic regression. Population attributable fractions were estimated for key predictors. Results Delayed immunization was significantly associated with indicators of social disadvantage as well as parental disagreement with immunization. Attributable fractions for delayed immunization included lone motherhood (3.8%; 95% confidence interval CI [0.8, 6.7]), larger family size (39.5%; 95% CI [31.2, 46.8]), residential mobility (3.3%; 95% CI [0.1, 6.5]), lack of private hospital insurance (9.4%; 95% CI [0.7, 17.3]), a medical condition in the child (2.0%; 95% CI [0.2, 3.9]), and parental disagreement with immunization (2.1%; 95% CI [0.3, 3.9]). Conclusions Parental attitudes accounted for a relatively small percentage of delayed infant immunization. In contrast, many children who did not receive vaccines on time were characterized by social disadvantage, especially larger family size. Researchers and policy‐makers should consider how to make timely immunization easier for busy parents