The effects of income level on susceptibility to COVID-19 and COVID-19 morbidity/mortality: A nationwide cohort study in South Korea (Preprint)

BACKGROUND Low economic status has been highlighted as a factor affecting vulnerability to COVID-19 infection. OBJECTIVE This study aimed to investigate the association of income level with susceptibility to coronavirus disease 2019 (COVID-19) and COVID-19 morbidity and mortality. METHODS Using the Korea National Health Insurance COVID-19 Database cohort, medical claim data from 2015 through 2020 were collected. A total of 7,943 patients who were diagnosed with COVID-19 from 1 January 2020 to 4 June 2020 were included. A total of 118,914 participants had negative COVID-19 PCR tests. Income levels were classified by 20th percentiles based on 2019 Korean National Health Insurance premiums. The 20th percentile income levels were categorized into three groups (low, middle, and high). The relation of income level with susceptibility to COVID-19 and COVID-19 morbidity and mortality was analyzed using logistic regression analysis adjusted for age, sex, Charlson Comorbidity Index (CCI), and hypertension. Subgroup analyses were conducted according to age, sex, CCI score, and history of hypertension. RESULTS A high income level was related to lower odds of COVID-19 infection (adjusted odds ratio [aOR] = 0.79, 95% confidence interval [CI] = 0.75–0.83, P <.001). The negative association between income level and COVID-19 infection was maintained in all subgroups. Income level did not show an association with COVID-19 morbidity and mortality in the overall study population or in the subgroup analyses. CONCLUSIONS Patients with low income levels were susceptible to COVID-19 infection. However, there was no relation of COVID-19 morbidity and mortality with income level in the Korean population.