Low Vaccination Rates Put Socially Vulnerable at Risk for Severe COVID-19

Why do patients in socially vulnerable communities tend to have more severe cases of SARS-CoV-2? The answer is simpler than expected, according to a new study that found much of the greater symptom burden could be linked to lower uptake of effective vaccines and boosters. Here are more details.

ATLANTA – COVID-19 vaccination is as effective in communities with higher social vulnerability as more affluent ones but lower vaccine coverage means that residents of those areas are likely to have worse outcomes from infection, according to a new study from the national Centers for Disease Control and Prevention.

“We found that protection against emergency room and urgent care center visits, hospitalization and death conveyed by a COVID-19 mRNA vaccination did not vary by social vulnerability,” said study co-author Brian Dixon, PhD, MPA of the Regenstrief Institute in Indiana. “But because social vulnerability did play a role in whether individuals are vaccinated or not — and socially vulnerable communities have lesser vaccine coverage — socially vulnerable individuals and their communities are bearing a larger burden during the pandemic. They are having poorer outcomes as they are less likely to be vaccinated.”

The report in Clinical Infectious Diseases points out that exposure risk to SARS-CoV-2, as well as poor access to healthcare, are often linked with social vulnerability. The authors sought to determine if those factors had any bearing on observed vaccine effectiveness (VE). “Understanding whether these factors impact VE could contribute to our understanding of real-world VE,” they add.


To do that, the study team used electronic health record data from 7 health systems to assess vaccination coverage among patients with medically attended COVID-19-like illness. SVI rankings were determined by geocoding patient addresses to census tracts.

The report notes that, in July 2021, primary series vaccination coverage was higher in the least vulnerable quartile than in the most vulnerable quartile (56% vs 36%, respectively). In February 2022, booster dose coverage among those who had completed a primary series was higher in the least vulnerable quartile than in the most vulnerable quartile (43% vs 30%). “VE among 2-dose and 3-dose recipients during the Delta and Omicron BA.1 periods of predominance was similar across SVI quartiles,” according to the study.

“COVID-19 vaccination coverage varied substantially by SVI. Differences in VE estimates by SVI were minimal across groups after adjusting for baseline patient factors,” the authors explain. “However, lower vaccination coverage among more socially vulnerable groups means that the burden of illness is still disproportionately borne by the most socially vulnerable populations.”

The social vulnerability index (SVI) includes 15 attributes of social vulnerability across four themes: socioeconomic status, household composition and disability, minority status and language, and housing type and transportation. The study proposed that those elements could be associated with vaccination coverage and impact VE via mechanisms including:

  • Intensity and duration of SARS-CoV-2;

  • exposure (e.g. crowding, reliance on public transportation, occupational requirements; susceptibility to infection (eg, biological factors such as immune system response) and

  • access to healthcare or likelihood of seeking healthcare or testing in a hospital, emergency department, or urgent care clinic versus other settings (e.g...insurance status, access to telemedicine and at-home testing).

The VISION Network is a research network that evaluates COVID-19 vaccine effectiveness across diverse populations and geographic areas. In addition to Regenstrief Institute, other members are Columbia University Irving Medical Center, HealthPartners, Intermountain Healthcare, Kaiser Permanente Northern California, Kaiser Permanente Northwest and University of Colorado.

“Socially vulnerable individuals may live in densely populated buildings and neighborhoods, travel via crowded public transportation and often hold jobs that are not conducive to remote work. So, they are more susceptible to catching COVID,” said co-author Katie Allen, a data scientist with Regenstrief Institute. “And they may not have the resources to seek medical care when they are getting sick, leading to adverse medical outcomes.”

“Initial COVID-19 vaccination coverage remains lower in communities with higher social vulnerability and booster rates are even lower,” Dixon added. “This study shows the need to focus public health efforts on vaccine coverage as well as vaccine effectiveness.”