Context: Emerging evidence shows correlation between the presence of neutralization antibodies (nAbs) and protective immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Currently available commercial serology assays lack the ability to specifically identify nAbs. An ELISAbased nAb assay (GenScript cPass neutralization antibody assay) has recently received emergency use authorization from the Food and Drug Administration (FDA).
Objective: To evaluate the performance characteristics of this assay and compare and correlate it with the commercial assays that detect SARS-CoV-2 specific IgG.
Design: Specimens from SARS-COV-2 infected patients (n=124), healthy donors obtained pre-pandemic (n=100), and from patients with non-COVID (coronavirus disease 2019) respiratory infections (n=92) were analyzed using this assay. Samples with residual volume were also tested on three commercial serology platforms (Abbott, EUROIMMUN, Siemens). Twenty-eight randomly selected specimens from patients with COVID-19 and 10 healthy controls were subjected to a Plaque Reduction Neutralization Test (PRNT).
Results: The cPass assay exhibited 96.1% (95% CI, 94.9%–97.3%) sensitivity (at >14 days post- positive PCR), 100% (95% CI, 98.0%–100.0%) specificity and zero cross-reactivity for the presence of non- COVID respiratory infections. When compared to the plaque reduction assay, 97.4% (95% CI, 96.2%–98.5%) qualitative agreement and a positive correlation (R2 =0.76) was observed. Comparison of IgG signals from each of the commercial assays with the nAb results from PRNT/cPass assays displayed >94.7% qualitative agreement and correlations with R2=0.43/0.68 (Abbott), R2=0.57/0.85 (EUROIMMUN) and R2=0.39/0.63 (Siemens), respectively.
Conclusions: The combined data support the use of cPass assay for accurate detection of the nAb response. Positive IgG results from commercial assays associated reasonably with nAbs presence and can serve as a substitute.