Contributions of prior health and vaccination to inequality in COVID-19 mortality by income: analysis of administrative microdata for the non-institutionalized Dutch population.

BACKGROUND: The COVID-19 pandemic caused a large health burden that disproportionally fell on people with a lower socio-economic status. Not much is known about the role of structural differences in pre-existing health and vaccination uptake in explaining these inequalities. We aim to disentangle these factors and quantify their contribution to income-related inequality in COVID-19 mortality. METHODS: Using linked Dutch administrative microdata (N = 6 619 699), we model the risk of COVID-19 death based on pre-existing health and vaccination status for the entire population above the age of 50 years in 2021. Health is proxied by individual-level remaining life expectancy based on predictions by income using detailed information on demographics, specific outpatient medication(s), and hospital records. Building on this, we then quantify the extent to which differences in pre-existing health and vaccination status between lower and higher incomes explain income-related differences in COVID-19 deaths. RESULTS: We find strong income-related differences in COVID-19 mortality. In 2021, individuals of the poorest income quintile were about three times more likely to die of COVID-19 than those in the richest quintile. Differences in pre-existing health are more important than differences in vaccination uptake in explaining this gap. For the poorest males/females, 67%/46% can be explained by differences in health and 14%/19% by vaccination status. CONCLUSION: Differences in pre-existing health by income are likely the most important determinant of income-related inequality in COVID-19 mortality. These findings signal that policies focused on reducing existing inequalities in health might lessen the burden of future health crises.