Health disparities, leading to worse health outcomes such as elevated COVID-19 death rates, are rooted in social and structural factors. These disparities notably impact individuals from lower socioeconomic backgrounds and more socially vulnerable areas [1, 2]. Social vulnerability is defined as “the degree to which a community exhibits certain social conditions, including high poverty, low percentage of vehicle access, or crowded households, that may affect that community’s ability to prevent human suffering and financial loss in the event of a disaster” [3]. During the COVID-19 pandemic, racial and ethnic minorities were disproportionately impacted by COVID-19, experiencing higher rates of infection, hospitalization, and death compared to White people in the United States (U.S.) [4–9]. This can be attributed to preexisting health disparities such as limited access to healthcare [10] and a higher prevalence of underlying health conditions (e.g. heart disease, chronic kidney disease, chronic obstructive pulmonary disease, diabetes, and obesity) [11, 12]. Additionally, research from the first 2 years of the COVID-19 pandemic found that people who had no vehicle access [13, 14], limited English proficiency [14, 15], and certain living conditions, such as crowded households [14, 15], were at increased risk for COVID-19. Studies have also shown that people who lived in socially vulnerable areas had lower COVID-19 vaccination uptake [16–18], and treatments dispensed in 2022 [19]. When the COVID-19 pandemic began, researchers quickly focused on understanding the various factors that contributed to the disparities in infection and death rates. Early studies primarily emphasized social vulnerability but often did not include a comprehensive analysis of medical vulnerability and healthcare infrastructure [13–16, 20]. This study expands the analysis by exploring the lasting effects of social vulnerability on COVID-19 outcomes throughout the later phases of the pandemic using a health equity perspective. Even though the COVID-19 public health emergency has ended, the SARS-CoV-2 virus continues to circulate. Examining the relationship between death and social vulnerability can inform initiatives aimed at reducing health disparities, including efforts related to vaccination and treatment.

The CDC/ATSDR Social Vulnerability Index (SVI) was developed as a place-based index, database and mapping tool to assist public health officials with identifying and quantifying socially vulnerable communities [3]. Public health officials and community leaders have used SVI data to prepare communities to respond to emergencies, especially during the COVID-19 pandemic. The CDC/ATSDR SVI ranks each county on 16 social factors and groups them into four related themes: socioeconomic status, household characteristics, racial and ethnic minority status, and housing type and transportation (Fig. 1). In 2021, the U.S. Department of Health and Human Services (HHS) Office of Minority Health partnered with the CDC/ATSDR to develop the Minority Health Social Vulnerability Index (MHSVI). The Minority Health Social Vulnerability Index (MHSVI) builds upon the CDC/ATSDR SVI by incorporating two additional variables, medical vulnerability, and healthcare infrastructure. By considering these aspects, the MHSVI provides a more comprehensive assessment of social vulnerability, especially for minority populations [21]. The purpose of this study is to analyze the relationship between COVID-19 deaths and social vulnerability using the MHSVI.

Among all counties, the mean percentage of the population living below the poverty line was 24.5% (range 3.7–71%) within the SES theme and the mean percentage of persons ages 65 and older was 19.2% (range 3–57.8%) within the HC theme. Within the REMS theme, on average, about 24.2% (range 0–98.9%), the sum of the average each racial and ethnic minority group, of the population identified as a racial or ethnic minority across all U.S. counties (Table 1).

Table 2 shows COVID-19 deaths, death rates, and rate ratios by quartile, with the first quartile being the least vulnerable and the fourth quartile being the most vulnerable. Among 3089 U.S. counties, the cumulative number of COVID-19 deaths between January 1, 2020 through June 24, 2023 was 1,134,272. For the overall index ranking, the adjusted rate ratio of COVID-19 deaths in the second, third, and fourth quartiles were 1.06 (95% CI 0.99–1.13), 1.14 (95% CI 1.06–1.22), and 1.41 (95% CI 1.31–1.52) higher, respectively, compared to the death rate for counties in the least vulnerable quartile (Fig. 2). For the SES theme, the adjusted COVID-19 death rate ratios for counties in the second, third, and most vulnerable quartiles were 1.14 (95% CI 1.06–1.21), 1.29 (95% CI 1.20–1.38), and 1.39 (95% CI 1.28–1.50) higher, respectively, compared to the death rate for counties in the least vulnerable quartile (Fig. 3). For the HC theme, the adjusted COVID-19 death rates for counties in the second, third, and most vulnerable quartile were 1.14 (95% CI 1.07–1.21), 1.32 (95% CI 1.24–1.41), and 1.47 (95% CI 1.37–1.57) higher respectively, compared to the death rate for counties in the least vulnerable quartile (Fig. 4). The REMS theme had adjusted rates of 1.10 (95% CI 1.03–1.17), 1.26 (95% CI 1.18–1.34), and 1.44 (95% CI 1.34–1.55) for the same quartiles (Fig. 5). The HTT theme had adjusted rates of 1.18 (95% CI 1.11–1.26), 1.36 (95% CI 1.28–1.45), and 1.55 (95% CI 1.46–1.66) (Fig. 6). In contrast, counties of high vulnerability generally had lower COVID-19 deaths compared to counties with low vulnerability for the HIA theme with adjusted rates of 0.74 (95% CI 0.71–0.78), 0.59 (95% CI 0.56–0.62), and 0.42 (95% CI 0.39–0.44) for the second, third, and most vulnerable quartiles, respectively (Fig. 7). For the MV theme, the adjusted COVID-19 death rate ratios for counties in the second, third, and most vulnerable quartiles were 1.12 (95% CI 1.05–1.19), 1.22 (95% CI 1.14–1.30), and 1.35 (95% CI 1.25–1.45) higher, respectively, compared to the death rate for counties in the least vulnerable quartile (Fig. 8).

Table 3 shows that the HTT, HIA, and MV themes were associated with COVID-19 death rates. For the HTT theme, one decile increase in percentile rank was associated with 1.02 times (95% CI 1.01–1.03) increase in death rates. Increasing percentile rank by one decile was associated with 1.04 times (95% CI 1.03–1.05) increase in death rates for the MV theme. There was an opposite trend for the HIA theme, where every decile increase in percentile rank was associated with 0.90 times (95% CI 0.89–0.90) decrease in COVID-19 death rates. Though the association between the HC theme and COVID-19 death rates was statistically significant, the confidence interval rounds to 1.0. Therefore, we did not consider this association practically significant for further discussion.

This study contributes significant new insights into the associations between social vulnerability and COVID-19 death rates across the U.S. We explored the association between U.S. COVID-19 deaths and various themes of social vulnerability as described by the MHSVI. Counties of high vulnerability generally had higher COVID-19 death rates compared to counties with low vulnerability for socioeconomic status, household characteristics, racial and ethnic minority status, housing type and transportation, and medical vulnerability indicators. The association between higher COVID-19 death rates and greater socioeconomic vulnerability in communities is confirmed by several studies [14, 15]. However, one study found temporal trend differences in COVID-19 outcomes with more vulnerable counties having lower death rates in October 2020 [25]. These findings contribute to the body of research, enhancing our understanding of how SES factors influence disparities in COVID-19 outcomes and highlighting the significant impact of structural inequities during the pandemic. The relationships between the SES factors, which include poverty, housing cost burden, no high school diploma and no health insurance, and COVID-19 deaths potentially reflect the multidimensional barriers, such as access to resources and healthcare, that potentiate disease risks and consequences in disproportionately affected populations [26]. However, when adjusting for the other five themes in the same model, we observed that the SES theme was no longer associated with COVID-19 deaths. We hypothesize the association went away because the SES theme is likely correlated with other themes such that the association was better captured in other themes or other themes have particularly unique relationships with death rates such that significance between the SES theme and death rates is lost.

During the pandemic, urban areas experienced a decline in deaths early in the pandemic, while rural areas witnessed higher rates of death and infection subsequently [27, 28]. We found that counties with a higher concentration of racial and ethnic minorities experienced higher COVID-19 deaths when compared to least vulnerable counties. We attribute this association to higher proportions of racial and ethnic minorities living in more metro and urban counties, which tend to have higher populations overall compared to rural areas [29]. These geographic differences present unique challenges and opportunities for public health professionals, as such public health professionals should consider the specific needs and circumstances of each community to enhance equitable health outcomes. The association between the REMS theme and COVID-19 deaths was no longer statistically significant when all themes were included in the model likely due to other themes better capturing the association when adjusting for all other themes.

Counties with higher social vulnerability, particularly in terms of the HC theme, experienced higher COVID-19 death rates compared to those less vulnerable. The HC theme includes several demographic factors that influence a community’s susceptibility to severe outcomes from COVID-19. Among these factors are age, disability status, household composition, and language proficiency. Older adults, specifically those over 65 years of age, are particularly at increased risk of severe COVID-19 outcomes due to age-related health vulnerabilities and pre-existing conditions [30]. In contrast, children under 17 years of age, who are part of this theme, typically experience milder symptoms or remain asymptomatic [31], though their inclusion highlights their role in community transmission dynamics. Individuals with disabilities face increased risk because of potential pre-existing health conditions and barriers to accessing healthcare [32]. Single-parent households may encounter additional stressors and challenges in accessing healthcare, which can impact their ability to manage health risks effectively. Furthermore, individuals with limited English proficiency often face language barriers that can hinder access to crucial health information and services, delaying medical care and complicating understanding of public health guidelines [14, 15, 33]. Effective communication strategies must address language barriers by providing health information in multiple languages and culturally relevant formats. This can improve understanding and adherence with public health guidelines. Public health strategies should prioritize disproportionately affected groups, particularly older adults, individuals with disabilities, single-parent households, and those with limited English proficiency. Tailored interventions can help mitigate severe outcomes and improve access to care.

After adjusting for all themes simultaneously, counties with high vulnerability in the HTT, MV, and HIA themes were associated with COVID-19 deaths. HTT indicators of the MHSVI include factors such as crowding, vehicle unavailability, and living in group quarters, indicating the degree of potential vulnerability or resilience of a community with respect to, housing and transportation resources. COVID-19 death rates increased progressively with each higher vulnerability quartile compared to counties in the least vulnerable quartile, highlighting a clear association between increased housing and transportation vulnerability and higher death rates on community health outcomes during the pandemic. Studies have shown that living conditions, such as overcrowding, are crucial factors in determining COVID-19 death risks, as such factors create challenging environments for quarantine and/or isolation within a household [34, 35]. Additionally, households with no vehicle access also faced increased risks [13, 14], suggesting that reliance on public transportation could potentially increase COVID-19 transmission risk, particularly in urban areas [36, 37].

There was also an association between COVID-19 deaths and the MV theme where counties with higher rates of cardiovascular disease, chronic respiratory diseases, obesity, diabetes, and/or the highest percentage of individuals with no internet access experienced increased rates of COVID-deaths. Other studies have confirmed the correlation between COVID-19 deaths, comorbidities, and community-level access to the internet [32, 38–40]. For the HIA theme, which encompasses factors such as the availability of medical facilities, more vulnerable counties had less risk of death compared to counties in the least vulnerable quartile. Vulnerable counties may have benefitted from targeted vaccine programs, potentially contributing to their lower death rates [41]. However, despite these targeted vaccination efforts, studies have demonstrated low vaccine uptake in high socially vulnerable counties, indicating that other factors may also influence these outcomes [16–18]. This discrepancy underscores the need for further investigation to identify the specific interventions that were most effective and to understand how these findings can be applied to future public health strategies. Investments in healthcare infrastructure and targeted interventions in under-resourced communities are vital for enhancing health outcomes, but additional research is necessary to refine these approaches and enhance their impact.

Geographic variations in social vulnerability and COVID-19 deaths revealed several notable trends. For the overall social vulnerability index ranking, counties with high overall social vulnerability and low death rates tended to be in the West whereas counties with high overall social vulnerability and high death rates tended to be in the Southeast (Fig. 2). For the SES theme, counties with low social vulnerability and high death rates were in the Midwest and Northeast while counties with high death rates and high social vulnerability were in the South and West U.S. regions (Fig. 3). For the HC theme, counties with higher social vulnerability and low death rates were in the western region of the country (Fig. 4). For the REMS themes, counties with high social vulnerability and low death rates were largely in the western region and Mid-Atlantic coastal area of the country. Counties with low social vulnerability and high death rates were clustered in the Midwest and some areas in the Southeast (Fig. 5). For the HTT theme, counties with high social vulnerability and low death rates were in the West (Fig. 6). For the HIA theme, there were many regions throughout the country with counties of low social vulnerability and high death rates (Fig. 7). For the MV theme, counties with high death rates and high social vulnerability tended to be in the Southeast region (Fig. 8). These patterns underscore the complex interplay between regional factors and social vulnerability in influencing COVID-19 death rates across different U.S. regions.

In conclusion, counties with higher social vulnerability experienced greater COVID-19 death rates. This highlights the need for targeted interventions and comprehensive strategies to reduce health disparities and enhance resilience in disproportionately affected populations during public health crises.