Objective: To compare demographic, social, maternal, and infant related factors associated with partial immunisation and no immunisation in the first year of life in the United Kingdom.
Design: Prospective cohort study.
Setting: Sample of electoral wards in England, Wales, Scotland, and Northern Ireland, stratified by measures of ethnic composition and social disadvantage.
Participants: 18,488 infants born between September 2000 and January 2002, resident in the UK and eligible to receive child benefit (a universal benefit available to all families) at age 9 months.
Main outcome measure: Immunisation status at 9 months of age, defined as fully immunised, partially immunised, or not immunised.
Results: Overall in the UK, 3.3% of infants were partially immunised and 1.1% were unimmunised; these rates were highest in England (3.6% and 1.3%, respectively; P < 0.01). Residence in ethnic or disadvantaged wards, larger family size, lone or teenaged parenthood, maternal smoking in pregnancy, and admission to hospital by 9 months of age were independently associated with partial immunisation status. In contrast, a higher proportion of mothers of unimmunised infants were educated to degree level or above (1.9%), were older (3.1%), or were of black Caribbean ethnicity (4.7%).
Conclusions: Mothers of unimmunised infants differ in terms of age and education from those of partially immunised infants. Interventions to reduce incomplete immunisation in infancy need different approaches.