key: cord-0692029-ce1umi53
authors: Cerutti, Helena; Bandini, Tommaso; Castria, Marinunzia; Cartocci, Alessandra; Ricci, Veronica; Tornesi, Stefania; Bogi, Alessia; Tesi, Giulia; Soldatini, Claudia; Toppi, Simona; Brogi, Alessandra
title: A quantitative assay for detection of SARS-CoV-2 neutralizing antibodies
date: 2022-01-02
journal: J Clin Virol
DOI: 10.1016/j.jcv.2021.105064
sha: 40bbada955afddd02b202f4dadfbce1664439799
doc_id: 692029
cord_uid: ce1umi53

OBJECTIVES: : Serological assays for SARS-CoV-2 have a critical role not only in diagnosis of COVID-19, but also in assessing the degree and duration of response of specific antibodies against the virus obtained through infection or vaccination. We present the results obtained with a competitive immunoenzymatic method (Chorus SARS-CoV-2 “Neutralizing” Ab) for quantitative determination of total neutralizing anti-S1 SARS-CoV-2 antibodies (IgG, IgM, and IgA) in human serum obtained on a disposable device with the Chorus TRIO instrument using a recombinant strong neutralizing antibody as tracer. METHODS: : A total of 694 sera were evaluated for SARS-CoV-2 neutralizing antibodies: 407 uninfected, 201 symptomatic subjects, 37 post-infection patients, and 49 vaccinated. Sixty-eight of the previous sera were used to compare the Chorus SARS-CoV-2 “Neutralizing” Ab results with those obtained with micro-neutralization of the Alpha and original variants. A set of 74 positive sera for other respiratory infections were analyzed to evaluate the possible cross reaction to SARS-CoV-2 virus. RESULTS: : Of the 694 samples, only 3 had discordant results between micro-neutralization and values measured by Chorus SARS-CoV-2 “Neutralizing” Ab: 1 false negative and 2 false positives. Values of sensitivity and specificity were very high: percent positive agreement (sensitivity) 99.6% (95% CI: 97.7 - 99.9) and percent negative agreement (specificity) 99.6% (95% CI: 98.0 -99.9). Concordance was high with a Gwet's Ac1 of 0.992. No significant differences were observed between the alpha and original variants. CONCLUSIONS: : The Chorus SARS-CoV-2 “Neutralizing” Ab test was highly sensitive and specific, and varies from most other currently available tests since it analyzes only antibodies with viral-neutralizing capacity.

Antibodies against SARS-CoV-2 play a central role in clearing the virus from infected 65 patients. To prevent COVID-19, antibodies should be able to engage the S1 subunit of SARS-CoV-66 2 spike protein, which contains the receptor binding domain (RBD) to angiotensin-converting 67 enzyme (ACE) 2, and neutralize the virus [1] . It has been extensively reported that the degree of the 68 antibody response correlates with the severity of COVID-19 and that the quantity of neutralizing 69 antibodies declines rather rapidly with time [2] [3] [4] . 70 Serological assays for SARS-CoV-2 play a role in diagnosis of COVID-19, in understanding 71 viral epidemiology and screening convalescent sera for therapeutic and prophylactic purposes, to 72 better understand the immune response to the virus, and to assess the degree and duration of the 73 response of specific antibodies [5] [6] [7] . Moreover, serological assays are of major importance in antibody detection [11] .

Among the many neutralizing antibodies from COVID-19 survivors, it has been shown that 88 the most potent recognize the spike protein RBD, followed by antibodies that recognize the S1 89 domain, spike protein trimer, and S2 subunit [12] . Monitoring the total anti-S1 antibody titer can The Chorus SARS-CoV-2 "Neutralizing" Ab assay is a competitive binding 108 immunoenzymatic assay. SARS-CoV-2 anti-S1 total antibodies present in the test sample (IgG, 3 days to evaluate the presence of a cytopathic effect (CPE). End-point titers were calculated using blind. Data were analyzed by a Diesse researcher who did not take part in the laboratory tests. 

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