Assay Harmonization Study To Measure Immune Response to SARS-CoV-2 Infection and Vaccines: a Serology Methods Study

Abstract

The Coronavirus disease 2019 (COVID-19) pandemic presented the scientific community with an immediate need for accurate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serology assays, resulting in an expansion of assay development, some without following a rigorous quality control and validation, and with a wide range of performance characteristics. Vast amounts of data have been gathered on SARS-CoV-2 antibody response; however, performance and ability to compare the results have been challenging. This study seeks to analyze the reliability, sensitivity, specificity, and reproducibility of a set of widely used commercial, in-house, and neutralization serology assays, as well as provide evidence for the feasibility of using the World Health Organization (WHO) International Standard (IS) as a harmonization tool. This study also seeks to demonstrate that binding immunoassays may serve as a practical alternative for the serological study of large sample sets in lieu of expensive, complex, and less reproducible neutralization assays. In this study, commercial assays demonstrated the highest specificity, while in-house assays excelled in antibody sensitivity. As expected, neutralization assays demonstrated high levels of variability but overall good correlations with binding immunoassays, suggesting that binding may be reasonably accurate as well as practical for the study of SARS-CoV-2 serology. All three assay types performed well after WHO IS standardization. The results of this study demonstrate there are high performing serology assays available to the scientific community to rigorously dissect antibody responses to infection and vaccination. IMPORTANCE Previous studies have shown significant variability in SARS-CoV-2 antibody serology assays, highlighting the need for evaluation and comparison of these assays using the same set of samples covering a wide range of antibody responses induced by infection or vaccination. This study demonstrated that there are high performing assays that can be used reliably to evaluate immune responses to SARS-CoV-2 in the context of infection and vaccination. This study also demonstrated the feasibility of harmonizing these assays against the International Standard and provided evidence that the binding immunoassays may have high enough correlation with the neutralization assays to serve as a practical proxy. These results represent an important step in standardizing and harmonizing the many different serological assays used to evaluate COVID-19 immune responses in the population.

Keywords: SARS-CoV-2; antibodies; harmonization; serology.

FIG 1

Sensitivity and specificity measurements of commercial, in-house, and neutralization serological assays. Graphical representation of the sensitivity and specificity of all tested assays. Specificity ≥93% and sensitivity ≥90% were considered acceptable. Data analysis was performed prior to harmonization.

FIG 2

Commercial, in-house, and neutralization assay measurement of the US Serology Standard after harmonization with the WHO International Standard. Commercial (A), in-house (B), and neutralization (C) assays were harmonized with the WHO International Standard and then used to measure the US Serology Standard. These measurements were then compared to the calibrated value of the US Serological Standard as shown by the red dashed line in each graph.

FIG 3

Pearson correlation of commercial and in-house serological assays versus neutralization assays. The commercial (A) and in-house (B) assay measures were compared to the neutralization assay results to calculate the Pearson correlation.