Objective: To investigate the relationship between primary immunisation status and MMR uptake
Design: Nationally representative, Millennium Cohort Study
Setting: Children born in the UK, 2000-2002 Participants: 14,578 children with immunisation data
Main outcome measures: MMR status at 3 years, defined as "immunised with MMR", "immunised with at least one single antigen vaccine", and "unimmunised"
Results: 88.6% of children had been immunised with MMR, 5.2% had received at least one of the single antigen vaccines and 6.1% were unimmunised against measles, mumps and rubella at age 3 years. Children who were unimmunised with the primary vaccines at ages 9 months (1.2%, n=168) and at three years (0.4%. n=67) were 13 (95% confidence interval: 10.8, 14.7) and 17 (14.6, 19.7) times more likely to be unimmunised against measles, mumps and rubella, compared with children who were fully immunised. They were also more likely to be immunised with at least one of the single antigen vaccines with risk ratios (RR) of 2.8 (1.2, 6.1) and 4.3 (1.8, 10.1). Similar but smaller associations were observed if children were partially immunised with the primary vaccines at 9 months (3.5%, n=504) and three years (3.6%, n=522) with risk ratios of 4.0 (3.2, 4.9) and 5.2 (4.2, 6.1) for no MMR immunisation, and 2.0 (1.1, 3.6) and 1.6 (1.1, 2.5) for single antigen vaccine use.
Conclusion: Children who remain unimmunised with primary vaccines are also more likely not to receive MMR. More work is needed to determine how best to target this group.