A Cross-Sectional Study of SARS-CoV-2 Seroprevalence between Fall 2020 and February 2021 in Allegheny County, Western Pennsylvania, USA

Abstract

Seroprevalence studies are important for understanding the dynamics of local virus transmission and evaluating community immunity. To assess the seroprevalence for SARS-CoV-2 in Allegheny County, an urban/suburban county in Western PA, 393 human blood samples collected in Fall 2020 and February 2021 were examined for spike protein receptor-binding domain (RBD) and nucleocapsid protein (N) antibodies. All RBD-positive samples were evaluated for virus-specific neutralization activity. Our results showed a seroprevalence of 5.5% by RBD ELISA, 4.5% by N ELISA, and 2.5% for both in Fall 2020, which increased to 24.7% by RBD ELISA, 14.9% by N ELISA, and 12.9% for both in February 2021. Neutralization titer was significantly correlated with RBD titer but not with N titer. Using these two assays, we were able to distinguish infected from vaccinated individuals. In the February cohort, higher median income and white race were associated with serological findings consistent with vaccination. This study demonstrates a 4.5-fold increase in SARS-CoV-2 seroprevalence from Fall 2020 to February 2021 in Allegheny County, PA, due to increased incidence of both natural disease and vaccination. Future seroprevalence studies will need to include the effect of vaccination on assay results and incorporate non-vaccine antigens in serological assessments.

Impact of maternal SARS-CoV-2 booster vaccination on blood and breastmilk antibodies

“…[ 18 ] SARS-CoV-2 RBD IgG and IgA ELISA were performed as described with modifications defined in Supplemental Material. [ 19 ] This assay was optimized to detect anti-SARS-CoV-2 RBD IgG (cut-off titer ≥ 900) with sensitivity of 94.8% and specificity of 97.8% and IgA (cut-off titer ≥ 300) with sensitivity of 88.2% and specificity of 97.3% in blood. The limit of detection on this assay was 100; samples below the limit were set to 99 for statistical analysis.…”

A Mycobacteriophage-Based Vaccine Platform: SARS-CoV-2 Antigen Expression and Display

“…Neutralization tests were performed as previously described [40]. Sera from a nonhuman primate previously vaccinated against SARS-CoV-2 and known to neutralize virus in this assay was included as a positive control.…”

What Do Antibody Studies Tell Us about Viral Infections?

“…In this Special Issue, five different publications [ 38 , 39 , 40 , 41 , 42 ] have characterized the antibody response at population and molecular levels, contributing to a broader picture of SARS-CoV-2 epidemiology. Xiao et al [ 38 ] conducted a large-scale screening of serum samples in the Guangdong province, China, between March and June 2020.…”

“…The overall prevalence of virus-specific antibodies was low soon after the emergence of COVID-19 in Guangdong, suggesting an urgent need for vaccination to increase population immunity to SARS-CoV-2. Another study by Xu et al [ 39 ] revealed a 4.5-fold increase in SARS-CoV-2 seroprevalence from Fall 2020 to February 2021 in the population of Western Pennsylvania, USA, which was shown to be driven both by infection and vaccination. Kazachinskaia et al [ 40 ] analyzed the blood samples of COVID-19 patients in Novosibirsk city, Russia, and observed cross-reactivity of antibodies to SARS-CoV (2002) proteins.…”