Social vulnerability and the risk of respiratory virus infection in households: a case-ascertained study

This study examines whether the Social Vulnerability Index (SVI), a location-based composite measure of social vulnerability, is associated with the risk of SARS-CoV-2 or influenza infection within households. Prospective cohort case-ascertained household transmission study. We analyzed data from a case-ascertained household transmission study conducted across multiple U.S. sites (September 2021–May 2023). Household contacts of index cases with confirmed infections self-collected nasal swabs daily for ten days, tested via RT-PCR for SARS-CoV-2 or influenza. Age, sex, and vaccine receipt were self-reported, with vaccination verified. Household addresses were geocoded to 2020 census tracts and linked to the national SVI percentile. Using modified Poisson regression models with generalized estimating equations, we assessed associations between census tract-level SVI and infection risk, adjusting for age, sex, vaccine receipt, and clustering by census tract. Participants included household contacts of index cases with SARS-CoV-2 (793 households, 1,408 participants) or influenza (273 households, 512 participants). We found that higher overall SVI was associated with increased SARS-CoV-2 infection risk (adjusted Incidence risk ratio [aIRR] 1.24; 95% CI: 1.00, 1.52). Specifically, the socioeconomic SVI domain was linked to higher infection risk (aIRR = 1.24; 95% CI: 1.02, 1.51). Other SVI domains were not statistically significant. For influenza, SVI was overall associated with greater infection, but confidence intervals crossed the null (aIRR = 1.45; 95% CI: 0.88, 2.39). Household contacts of SARS-CoV-2 index cases in high-SVI areas faced an increased risk of infection. No significant association was found for influenza, likely due to the small sample size. Increased access to SARS-CoV-2 testing, treatment, and preventive measures (e.g., masking, handwashing, isolation) may be especially important in high-SVI areas.