Social Vulnerability and Rurality Associated With Higher SARS-CoV-2 Infection-Induced Seroprevalence: A Nationwide Blood Donor Study, United States, July 2020 – June 2021 (preprint)

Background: Most studies on health disparities during COVID-19 pandemic focused on reported cases and deaths and were limited in capturing disparities in true infection rates or the impact of social determinants of health. This nationwide study aimed to examine SARS-CoV-2 (the virus that causes COVID-19) antibody seroprevalence in the U.S. and its associations with rurality and social vulnerability over time.Methods: This repeated cross-sectional study used data from blood donations made July 2020 - June 2021 in 50 states and Washington, D.C. Donor ZIP codes were matched to counties and linked with Social Vulnerability Index (SVI) and urban-rural classification. SARS-CoV-2 antibody seroprevalences induced by infection and infection-vaccination combined were estimated. Association of infection-induced seropositivity with demographics, rurality, SVI, and its four themes were quantified using stratified analyses and multivariate regression models.Findings: Weighted seroprevalence differed significantly by race/ethnicity, age, rurality, and social vulnerability with distinct temporal trends. From July 2020 to June 2021, infection-induced seroprevalence increased from 1.6% to 27.2% in rural counties and from 3.7% to 20.0% in urban counties. However, in June 2021, the combined infection- and vaccination-induced seroprevalence in rural counties was lower (80.0% vs. 88.1%). Adjusting for covariates, higher infection-induced seropositivity was associated with being Hispanic and non-Hispanic Black, younger, and living in rural or higher socially vulnerable counties.Interpretation: The findings demonstrated continuously increasing SARS-CoV-2 seroprevalence in the U.S. across all geographic, demographic, and social sectors. Infection-induced seroprevalence rates were consistently higher among Hispanic and non-Hispanic Black donors, and those from rural or socially vulnerable counties. Vaccine-induced seroprevalence was lower in rural counties than urban counties. The findings illustrated disparities in SARS-CoV-2 infections in the U.S. independent of case-based surveillance and testing availability, identified areas for targeted vaccination strategies, and can inform efforts to reduce inequities and prepare for future outbreaks.Funding Information: This analysis did not have external funding sourcesDeclaration of Interests: All coauthors declare no conflict of interests. Ethics Approval Statement: The study was approved by CDC as non-research public health surveillance based on anonymization of data and routine consent for blood donation testing that includes use of residual samples for research purposes. The study does not require human-subject research review nor clearance by the Office of Management and Budget and was conducted consistent with applicable federal law and CDC policy.

Use of U.S. Blood Donors for National Serosurveillance of SARS-CoV-2 Antibodies: Basis for an Expanded National Donor Serosurveillance Program. (preprint)

Introduction: The REDS-IV-P Epidemiology, Surveillance and Preparedness of the Novel SARS-CoV-2 Epidemic (RESPONSE) seroprevalence study conducted monthly cross-sectional testing for SARS-CoV-2 antibodies on blood donors in six U.S. metropolitan regions to estimate the extent of SARS-COV-2 infections over time. Study Design/Methods During March-August 2020, approximately [≥]1,000 serum specimens were collected monthly from each region and tested for SARS-CoV-2 antibodies using a well-validated algorithm. Regional seroprevalence estimates were weighted based on demographic differences with the general population. Seroprevalence was compared with reported COVID-19 case rates over time. Results/Findings: For all regions, seroprevalence was <1.0% in March 2020. New York experienced the biggest increase (peak seroprevalence, 15.8 % in May). All other regions experienced modest increases in seroprevalence(1-2% in May-June to 2-4% in July-August). Seroprevalence was higher in younger, non-Hispanic Black, and Hispanic donors. Temporal increases in donor seroprevalence correlated with reported case rates in each region. In August, 1.3-5.6 estimated cumulative infections (based on seroprevalence data) per COVID-19 case reported to CDC. Conclusion: Increases in seroprevalence were found in all regions, with the largest increase in New York. Seroprevalence was higher in non-Hispanic Black and Hispanic blood donors than in non-Hispanic White blood donors. SARS-CoV-2 antibody testing of blood donor samples can be used to estimate the seroprevalence in the general population by region and demographic group. The methods derived from the RESPONSE seroprevalence study served as the basis for expanding SARS-CoV-2 seroprevalence surveillance to all 50 states and Puerto Rico.