Background Cases of measles are rising in the United Kingdom (UK). While children are eligible for the first measles, mumps and rubella (MMR) vaccination at 12 months in the UK, coverage in the north-east London (NEL) region is the lowest in the UK, well below the 95% recommended to achieve herd immunity. It has been hypothesised that children who move home frequently are less likely to receive vaccinations. We examined the association between residential mobility, assessed by the number of general practice (GP)-recorded addresses in the first two years of life, and receipt of MMR vaccination by age two years.

Methods We derived households by linking the registered patient addresses of 177,451 children born in 2014-2019 and ever registered with a GP in NEL using pseudonymised Unique Property Reference Numbers (pUPRNs). We included 169,073 (95.3%; 51.1% male) children after excluding 8,378 without a GP registration or pUPRN at age 12 months. The primary outcome was receipt of MMR vaccination by age two years coded in the primary care electronic health record. Residential mobility was categorised as number of pUPRNs (1, 2, ≥3) between earliest GP registration and vaccination date or second birthday. We calculated the percentage of children receiving MMR by residential mobility category and estimated adjusted odds (aOR; 95% confidence intervals [CI]) for MMR receipt adjusting for sex, ethnicity, Index of Multiple Deprivation quintile, local authority, number of children in household, and household composition.

Results Overall, 139,866 (82.7%) children received MMR by age two, and 11,820 (7.0%) had more than one address. The proportion receiving MMR by age two decreased with increasing residential mobility: 83.3% (95% CI: 83.1,83.4), 77.2% (76.3,78.1), and 71.1% (69.4,72.7) for children with one, two, or three or more addresses respectively. In preliminary multivariable analyses, children with multiple addresses were less likely to receive MMR by age two compared to those with one address: aOR: 0.68 (0.64,0.72); 0.48 (0.44,0.53) for 2 and ≥3 addresses respectively. Further analyses are being carried out to adjust for number of children in the household and household generational composition.

Conclusion These preliminary findings suggest uptake of the first MMR vaccine by two years of age is lower in children with multiple addresses in the first two years of life. Strengths of our study include use of real-world data and a novel method of linking children in households using routine electronic health records. Further research is needed to identify actionable opportunities to improve uptake.