ABSTRACT
BackgroundSeroprevalence studies are important tools to estimate the prevalence of prior or recent SARS-CoV-2 infections, identifying hotspots and high-risk groups and informing public health responses to the COVID-19 pandemic. We conducted a city-level seroprevalence study in Holyoke, Massachusetts, USA to estimate the seroprevalence of SARS-CoV-2 antibodies and risk factors for seropositivity. MethodsWe invited inhabitants of 2,000 randomly sampled addresses between November 5 and December 31, 2020. Participants completed questionnaires measuring sociodemographic and health characteristics, and COVID-19 exposure history, and provided dried blood spots for measurement of SARS-CoV-2 IgG and IgM antibodies. We calculate total and subgroup seroprevalence estimates based on presence of IgG antibodies using a Bayesian procedure that incorporates uncertainty in antibody test sensitivity and specificity. We account for clustering by household and weighting based on demographic characteristics to ensure estimates represented the citys population. FindingsWe enrolled 280 households including 472 individuals. 328 underwent antibody testing. The citywide seroprevalence estimate of SARS-CoV-2 IgG was 13.1% (95%CI 6.9-22.3) compared to 9.8% based on publicly reported case counts. Seroprevalence was 16.1% (95%CI 6.2-31.8) among individuals identifying as Hispanic compared to 9.4% (95%CI 4.6-16.4) among those identifying as non-Hispanic white. Seroprevalence was higher among Spanish speaking households (21.9%; 95% CI 8.3-43.9) compared to English speaking households (10.2%; 95% CI 5.2-18.0) and among individuals living in high vulnerability areas (14.4%; 95% CI 7.1-25.5) compared to low vulnerability areas (8.2%; 95% CI 3.1-16.9). InterpretationThe measured SARS-CoV-2 seroprevalence of IgG antibodies in Holyoke was only 13.1% during the second surge of SARS-CoV-2 in this region, far from accepted thresholds for "herd immunity." Already vulnerable communities were at highest risk of prior infection. Implementation of local serosurveys in tandem with proactive public health interventions that address disparities in SARS-CoV-2 exposure are crucial to ensure at-risk communities have appropriate educational materials and access to vaccines, testing, and timely treatment. FundingThe Sullivan Family Foundation, Harvard Data Science Institute Bias2 program, the US Centers for Disease Control and Prevention.
