Do interventions that improve immunisation uptake also reduce social inequalities in uptake?

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Abstract
Objective: To investigate whether an intervention designed to improve overall immunisation uptake affected social inequalities in uptake. Design: Cross-sectional small area analyses measuring immunisation uptake in cohorts of children before and after intervention. Small areas classified into five groups, from most deprived to most affluent, with Townsend deprivation score of census enumeration districts. Setting: County of Northumberland. Subjects--All children born in county in four birth cohorts (1981-2, 1985-6, 1987-8, and 1990-1) and still resident at time of analysis. Main outcome measures: Overall uptake in each cohort of pertussis, diphtheria, and measles immunisation, difference in uptake between most deprived and most affluent areas, and odds ratio of uptake between deprived and affluent areas. Results: Coverage for pertussis immunisation rose from 53.4% in first cohort to 91.1% in final cohort. Coverage in the most deprived areas was lower than in the most affluent areas by 4.7%, 8.7%, 10.2%, and 7.0% respectively in successive cohorts, corresponding to an increase in odds ratio of uptake between deprived and affluent areas from 1.2 to 1.6 to 1.9 to 2.3. Coverage for diphtheria immunisation rose from 70.0% to 93.8%; differences between deprived and affluent areas changed from 8.6% to 8.3% to 9.0% to 5.5%, corresponding to odds ratios of 1.5, 2.0, 2.5, and 2.6. Coverage for measles immunisation rose from 52.5% to 91.4%; differences between deprived and affluent areas changed from 9.1% to 5.7% to 8.2% to 3.6%, corresponding to odds ratios of 1.4, 1.4, 1.7, and 1.5. Conclusion--Despite substantial increase in immunisation uptake, inequalities between deprived and affluent areas persisted or became wider. Any reduction in inequality occurred only after uptake in affluent areas approached 95%. Interventions that improve overall uptake of preventive measures are unlikely to reduce social inequalities in uptake.