Temporal trends in the association of social vulnerability and race/ethnicity with county-level COVID-19 incidence and outcomes in the USA: an ecological analysis

Abstract

Background: The COVID-19 pandemic adversely affected the socially vulnerable and minority communities in the USA initially, but the temporal trends during the year-long pandemic remain unknown.

Objective: We examined the temporal association of county-level Social Vulnerability Index (SVI), a percentile-based measure of social vulnerability to disasters, its subcomponents and race/ethnic composition with COVID-19 incidence and mortality in the USA in the year starting in March 2020.

Methods: Counties (n=3091) with ≥50 COVID-19 cases by 6 March 2021 were included in the study. Associations between SVI (and its subcomponents) and county-level racial composition with incidence and death per capita were assessed by fitting a negative-binomial mixed-effects model. This model was also used to examine potential time-varying associations between weekly number of cases/deaths and SVI or racial composition. Data were adjusted for percentage of population aged ≥65 years, state-level testing rate, comorbidities using the average Hierarchical Condition Category score, and environmental factors including average fine particulate matter of diameter ≥2.5 μm, temperature and precipitation.

Results: Higher SVI, indicative of greater social vulnerability, was independently associated with higher COVID-19 incidence (adjusted incidence rate ratio per 10 percentile increase: 1.02, 95% CI 1.02 to 1.03, p<0.001) and death per capita (1.04, 95% CI 1.04 to 1.05, p<0.001). SVI became an independent predictor of incidence starting from March 2020, but this association became weak or insignificant by the winter, a period that coincided with a sharp increase in infection rates and mortality, and when counties with higher proportion of white residents were disproportionately represented ('third wave'). By spring of 2021, SVI was again a predictor of COVID-19 outcomes. Counties with greater proportion of black residents also observed similar temporal trends in COVID-19-related adverse outcomes. Counties with greater proportion of Hispanic residents had worse outcomes throughout the duration of the analysis.

Conclusion: Except for the winter 'third wave', when majority of the white communities had the highest incidence of cases, counties with greater social vulnerability and proportionately higher minority populations experienced worse COVID-19 outcomes.

Keywords: COVID-19; epidemiology; public health; social medicine.

Figure 1

Temporal association between COVID-19 incidence and (A) county-level Social Vulnerability Index (SVI) and its subcomponents (B) socioeconomic status, (C) household composition and disability, (D) minority status and language, and (E) housing type and transportation between 22 March 2020 and 6 March 2021. The base model (red lines) is adjusted for proportion of population aged ≥65 years and state-level COVID-19 testing. The green lines are additionally adjusted for CMS average Hierarchical Condition Category score (proxy for comorbidities). The blue lines are additionally adjusted for environmental factors including average daily temperature (degrees Fahrenheit), average daily precipitation and average particulate matter of diameter ≥2.5 μm. Of note, the proportion aged ≥65 years was not included as a covariate for models for overall Social Vulnerability Index and household composition/disability because these indices contain the age variable. CMS, Centers for Medicare and Medicaid Services.

Figure 2

Temporal association between COVID-19 death per capita and (A) county-level Social Vulnerability Index and its subcomponents (B) socioeconomic status, (C) household composition and disability, (D) minority status and language, and (E) housing type and transportation between 22 March 2020 and 6 March 2021. The base model (red lines) is adjusted for proportion of population aged ≥65 years and state-level COVID-19 testing. The green lines are additionally adjusted for CMS average Hierarchical Condition Category score (proxy for comorbidities). The blue lines are additionally adjusted for environmental factors including average daily temperature (degrees Fahrenheit), average daily precipitation and average particulate matter of diameter ≥2.5 μm. Of note, the proportion aged ≥65 years was not included as a covariate for models for overall Social Vulnerability Index and household composition/disability because these indices contain the age variable. CMS, Centers for Medicare and Medicaid Services.

Figure 3

Temporal association of county-level racial composition (black, Hispanic/Latino, white) and COVID-19 (A) incidence and (B) death per capita between 22 March 2020 and 26 September 2020 after adjusting for proportion of population aged ≥65 years, state-level COVID-19 testing, CMS average Hierarchical Condition Category score (proxy for comorbidities), and environmental factors including average daily temperature (degrees Fahrenheit), average daily precipitation and average particulate matter of diameter ≥2.5 μm. CMS, Centers for Medicare and Medicaid Services.

Figure 4

County-level map of the USA showing (A) incidence and (B) death per capita for COVID-19 across three timepoints: July 2020, December 2020 and March 2021. County-level proportion of black, Hispanic/Latino and white residents is shown in (C). As shown, black and Hispanic residents are disproportionately represented in the southeast and southwestern USA, where outcomes were worst in July 2020 and again in March 2021. Midwestern states, where there are less diverse communities (higher proportion of white residents), showed worst outcomes in December 2020.