Do income inequality and social capital associate with measles-containing vaccine coverage rate?

Objective: We investigated the association between income inequality and social capital with measles-containing vaccine (MCV) coverage rates in Japan.

Methods: MCV coverage data for all 1750 municipalities were collected from statistics publicized by the Ministry of Health, Labour and Welfare of Japan in 2010. Prefectural Gini coefficients in 2009 (an indicator of income inequality) and social capital indicators (including voting rates, volunteer rates at the prefectural level, and move-in ratios at the municipal level) were linked to MCV coverage using a multilevel analysis adjusting for covariates (population, age distribution, average income, average number of household members).

Results: Coverage of the first dose of MCV (MCV1), and second dose (MCV2), decreased by 3.98% (95% confidence interval [CI]: 0.26-7.71) and 4.28% (95% CI: 0.60-7.60) per each 0.1-unit increase in Gini coefficients within large municipalities (with a population 50,000 or more), respectively. Conversely, coverage of MCV2 increased by 0.26% (95% CI: 0.08-0.45) per 1% increase in voting rate within large municipalities. Volunteer rates were inversely associated with MCV2 coverage within large municipalities. Move-in ratios at the municipal level were inversely associated with MCV2 coverage within medium-sized municipalities (with a population between 10,000 and 50,000).

Conclusions: While higher income inequality at a prefectural level was associated with lower MCV coverage rates, higher social capital was associated with higher coverage in large municipalities. To enhance MCV coverage in Japan, we recommend that income inequality be addressed and social capital boosted at the prefectural level.