Abstract
Seroprevalence studies are crucial both for estimating the prevalence of SARS-CoV-2 exposure and to provide a measure for the efficiency of the confinement measures. Portuguese universities were closed on March 16th 2020, when Portugal only registered 62 SARS-CoV-2 infection cases per million. We have validated a SARS-CoV-2 ELISA assay to a stabilized full-length spike protein using 216 pre-pandemic and 19 molecularly diagnosed SARS-CoV-2 positive individual's samples. At NOVA University of Lisbon, presential work was partially resumed on May 25th with staggered schedules. From June 15th to 30th, 3–4 weeks after the easing of confinement measures, we screened 1,636 collaborators of NOVA university of Lisbon for the presence of SARS-CoV-2 spike specific IgA and IgG antibodies. We found that spike-specific IgG in 50 of 1,636 participants (3.0%), none of which had anti-spike IgA antibodies. As participants self-reported as asymptomatic or paucisymptomatic, our study also provides a measurement of the prevalence of asymptomatic/paucisymptomatic SARS-CoV-2 infections. Our study suggests that essential workers have a 2-fold increase in viral exposure, when compared to non-essential workers that observed confinement. Additional serological surveys in different population subgroups will paint a broader picture of the effect of the confinement measures in the broader community.
Highlights
In late 2019, SARS-CoV-2 emerged as a novel human coronavirus, and its subsequent worldwide spread has led to ∼47,596,852 infections and to ∼1,216,357 deaths
Our serological assay uses the trimeric ectodomain of SARSCoV-2 spike protein as antigen and consists in a modified enzyme-linked immunosorbent assay (ELISA) protocol developed by Florian Krammer group at Mount Sinai’s CLIA laboratory where it received New York State Department of Health (NYSDOH) and FDA emergency use authorization [8, 9]
To set-up our ELISA assay we made use of serum from 19 individuals consulted at Hospital Fernando Fonseca that were diagnosed positive for SARS-CoV-2 infection by RT-PCR of nasopharyngeal and/or oropharyngeal swabs in a laboratory certified by the Portuguese National Health Authorities
Summary
In late 2019, SARS-CoV-2 emerged as a novel human coronavirus, and its subsequent worldwide spread has led to ∼47,596,852 infections and to ∼1,216,357 deaths (https://covid19.who.int). Spike is a trimeric glycoprotein protruding from SARS-CoV-2 viral membrane that mediates viral entry into the host cell [14, 15] These features make spike the preferential target in the development of serological tests and vaccine candidates. The serological assay used in this study to characterize anti-SARS-CoV-2 specific antibody response makes use of the trimerized, stabilized ectodomain of the spike protein. It is based on an enzyme-linked immunosorbent assay (ELISA) initially developed in early 2020 by Florian Krammer group at Mount Sinai’s CLIA laboratory where it received New York State Department of Health (NYSDOH) and FDA emergency use authorization [8, 9]
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