Performance of the Abbott SARS-CoV-2 IgG II Quantitative Antibody Assay Including the New Variants of Concern, VOC 202012/V1 (United Kingdom) and VOC 202012/V2 (South Africa), and First Steps towards Global Harmonization of COVID-19 Antibody Methods

Abstract

Background In the initial stages of the SARS-CoV-2 (COVID-19) pandemic a plethora of new serology tests were developed and introduced to the global market. Many were not evaluated rigorously and there is a significant lack of concordance in results across methods. To enable meaningful clinical decisions to be made, robustly evaluated, quantitative serology methods are needed. These should be harmonized to a primary reference material, allowing for the comparison of trial data and improved clinical decision making. Methods A comprehensive evaluation of the new Abbott IgG II anti-SARS-CoV-2 IgG method was undertaken using CLSI based protocols. Two different candidate primary reference materials and verification panels were assessed with a goal to moving towards harmonization. Results The Abbott IgG II method performs well across a wide range of parameters with excellent imprecision (<3.5%) and is linear throughout the positive range (tested to 38,365 AU/mL). The sensitivity (based on ≥14 day post positive RT-PCR samples) and specificity are 98.3% [90.6-100.0%] and 99.5% [97.1-100%] respectively. The candidate reference materials showed poor correlation across methods with mixed responses noted in methods that use the spike protein versus the nucleocapsid proteins as their binding antigen. Conclusions The Abbott IgG II anti-SARS-CoV-2 measurement appears to be the first linear method potentially capable of monitoring the immune response to natural infection, including from new emerging variants. The candidate reference materials assessed do not generate uniform results across several methods and further steps are needed to enable the harmonization process.

Evaluation of Three Quantitative Anti-SARS-CoV-2 Antibody Immunoassays

“…All three were highly specific, as previously reported for the Wantaï ( 16 – 18 ) and Alinity ( 19 ) assays. They accurately detected anti-SARS-CoV-2 antibodies in “early” sera, while the sensitivity of the Liaison and Alinity assays was lower for “late” sera.…”

Waning of Anti-spike Antibodies in AZD1222 (ChAdOx1) Vaccinated Healthcare Providers: A Prospective Longitudinal Study

“…The manufacturer-defined analytical measurement interval is 21 to 40,000 AU/mL, and the positivity cut-off is ≥50 AU/mL. This method has a sensitivity of 91.6% at all time points and 98.3% at >14 days; its specificity is 99.4% [16]. This method showed high concordance with the neutralizing antibody titer level with very high specificity [17].…”

“…Laboratory assay was completed using the Abbott Architect i2000SR immunoassay analyzer (Abbott Laboratories, Abbott Park, Illinois) following the manufacturer's package insert for the SARS-CoV-2 IgG II Quant assay [16]. It is used for the qualitative and quantitative determination of IgG antibodies to the RBD of the S1 subunit of the spike protein of SARS-CoV-2 in human serum and plasma.…”

Receptor binding domain‐IgG levels correlate with protection in residents facing SARS‐CoV‐2 B.1.1.7 outbreaks

“…However, the assay used in our study can probably be considered as a quantitative assay (<3.5% imprecision). 34 (ii) RBD‐IgG levels were measured within five days after the diagnosis of the first RT‐qPCR‐positive resident of the NH. Even if this delay was as short as possible, RBD‐IgG levels may also reflect a possible rapid anamnestic response to infection.…”