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Background: Given the effect of chronic diseases on risk of severe COVID-19 infection, the present pandemic may have a particularly profound impact on socially disadvantaged counties. Methods: Counties in the USA were categorised into five groups by level of social vulnerability, using the Social Vulnerability Index (a widely-used measure of social disadvantage) developed by the US Centers for Disease Control. The incidence and mortality from COVID-19, and the prevalence of major chronic conditions were calculated relative to the least vulnerable quintile using Poisson regression models. Results: Among 3141 counties, there were 5,010,496 cases and 161,058 deaths from COVID-19 by August 10, 2020. Relative to the least vulnerable quintile, counties in the most vulnerable quintile had twice the rates of COVID-19 cases and deaths (rate ratios 2.11 [95%CI: 1.97-2.26] and 2.42 [2.22-2.64], respectively). Similarly, the prevalence of major chronic conditions was 24-40% higher in the most vulnerable counties. Geographic clustering of counties with high COVID-19 mortality, high chronic disease prevalence and high social vulnerability was found, especially in southern USA. Conclusion: Some counties are experiencing a confluence of epidemics from COVID-19 and chronic diseases in the context of social disadvantage. Such counties are likely to require enhanced public health and social support.

Original publication




Journal article


Journal of Epidemiology and Community Health


BMJ Publishing Group

Publication Date



Covid-19, SARS-CoV-2, Syndemics, Inequality, Vulnerability, Chronic disease