Social inequalities in COVID-19 death by area-level income in 11.2 million people in Ontario, Canada: patterns over time and the mediating role of vaccination

Knowledge of patterns in COVID-19 deaths by area-level income over time and the mediating role of vaccination in inequality patterns remains limited. We used data from a population-based retrospective cohort of 11,248,572 adults in Ontario, Canada. Cause-specific hazard models were used examine the relationship between income 2016 Census at the dissemination area level) and COVID-19 deaths between March-1-2020 and January-30-2022, stratified by wave. We used regression-based causal mediation analyses to examine the mediating role of vaccination in the relationship between income and COVID-19 deaths during waves4 & 5. After accounting for demographics, baseline health, and other social determinants of health, inequalities in COVID-19 deaths by income persisted over time (hazard ratios[95% confidence intervals] comparing lowest-income vs. highest-income quintiles were 1.37[0.98-1.92] for wave-1, 1.21[0.99-1.48] for wave-2, 1.55[1.22-1.96] for wave-3, and 1.57[1.15-2.15] for waves4 & 5). By the start of wave four, 7,534,259(67.7%) of those alive were vaccinated, with lower odds of vaccination in the lowest-income vs. highest-income quintiles (0.71[0.70-0.71]). This inequality in vaccination accounted for 56.9%[22.5%-91.3%] of inequalities in COVID-19 deaths between individuals in the lowest-income vs. highest-income quintiles. Efforts are needed to address vaccination gaps and residual heightened risks associated with lower income to improve health equity in COVID-19 outcomes.