Elecsys anti sars cov 2 s

Four antibody binding assays were used for serological testing according to the instructions of the manufacturer. Two were quantitative: Abbott SARS-CoV-2 IgG II Quant-test (Abbott) (Abbott France, Rungis, France) with 50 arbitrary units (AU)/ml as a threshold for positivity, and Roche Elecsys anti-SARS-CoV-2 S (Roche Diagnostics France, Meylan, France) with 0.8 AU/ml used as a threshold for positivity. Two were semi-quantitative: Beckman Access SARS-CoV-2 IgG II (Beckman Coulter France SAS, Roissy CDG, France) with 30 AU/ml as a threshold for positivity and Siemens Atellica® IM SARS-CoV-2 IgG (Siemens Healthcare SAS, Saint-Denis, France) with 0.8 AU/ml used as a threshold for positivity.
BAU/ml proposed by the WHO, to standardize any assay to the WHO International Standard, were calculated by applying the following conversion factors as suggested by the manufacturers: Abbott, BAU/ml = (1/7) × Antibody Units (AU)/ml, Beckman, BAU/ml = 1 × AU/ml, Roche, BAU/ml = 1.029 × AU/ml, and Siemens, BAU/ml = 21.8 × AU/ml.
The neutralizing capacity was estimated by performing a surrogate virus neutralization test (sVNT) assay (GenScript, Piscataway, NJ, USA) as previously described [10 (link),15 (link),16 (link)]. This assay detects antibodies that block the interaction of SARS-CoV-2 with its entry receptor angiotensin-converting enzyme 2. A threshold of 20% was used for positivity.

Quantitative determination of pan-immunoglobulin to RBD of SARS-CoV-2 spike protein was achieved via automated electrochemiluminescence immunoassay using a Roche Elecsys anti-SARS-CoV-2 S (Roche Diagnostics, Basel, Switzerland; hereafter called Roche S). As previously described, the assay was performed on a Roche Cobas e601 system (Roche Diagnostics) and used plasma or serum from vaccinated volunteers for measurement [11 (link)]. This assay has a measuring range of 0.40 to 250 U/mL (up to 2500 U/mL with on-board 1:10 dilution). A concentration of <0.80 U/mL was considered negative and ≥0.80 U/mL was considered positive [12 (link)].

Our study population consisted of a cohort of SARS-CoV-2 seronegative healthcare workers of the Pederzoli Hospital of Peschiera del Garda (Verona, Italy), who voluntary accepted to be vaccinated with the mRNA-LNPs COVID-19 vaccine BNT162b2 (Comirnaty; Pfizer-BioNTech, NY, USA). Baseline seronegativity was confirmed the day before vaccination via routine monitoring with a Roche Elecsys Anti-SARS-CoV-2 S immunoassay, performed on a Roche Cobas 6000 (Roche Diagnostics, Basel, Switzerland; seronegativity defined as having anti-SARS-CoV-2 S total antibodies levels <0.8 U/L). A first dose of 30 μg of vaccine was administered between January 4 and 7, 2021, which was then followed by the second dose of 30 μg vaccine administered exactly 3 weeks after the first. All vaccines were prepared following manufacturer's recommendations and administered within 30 min from preparation. None of the subjects included in this study were taking immunosuppressive agents before vaccination. All subjects who participated in this retrospective observational study provided two separate written informed consents for being vaccinated and for inclusion in the post-vaccination anti-SARS-CoV-2 survey. This retrospective observational study was conducted in accordance with the Declaration of Helsinki and its protocol was cleared by the Ethics Committee of the Provinces of Verona and Rovigo (3246CESC).

Anti-spike (S) and anti-nucleocapsid (N) antibodies were measured using the Roche Elecsys® Anti-SARS-CoV-2 S and Roche Elecsys® Anti-SARS-CoV-2 N assays at the Public Health England (now the United Kingdom Health Security Agency) Laboratories at Porton Down, UK. The Roche S assay is reported in units per milliliter (U/ml), which are standardized 1:1 to the WHO binding antibody units/ml (BAU/ml). Seroconversion is defined for S as a response equal to or greater than 0.8 U/ml, and for N as a response equal to or greater than 1.0 COI.

The magnitude of anti-SARS-CoV-2 antibodies was measured using the Roche Elecsys AntiSARS-CoV-2 S and Roche Elecsys AntiSARS-CoV-2 N assays by the UKHSA Laboratories at Porton Down. The Roche assay measures the presence and the amount of serum antibodies to the spike RBD antigen of SARS-CoV-2. Seroconversion is defined as a response equal to or greater than 0.8 AU ml⁻¹, and no response is defined as less than 0.8 AU ml⁻¹. Low response was defined on the Roche anti-RBD Ig assay after evaluation of the serological response to vaccine in healthy controls. A cutoff for low was defined as the upper value of the bottom decile of healthy controls.