Commercial Serology Assays Predict Neutralization Activity Against SARS-CoV-2
Abstract
Background
Currently it is unknown whether a positive serology results correlates with protective immunity against SARS-CoV-2. There are also concerns regarding the low positive predictive value of SARS-CoV-2 serology tests, especially when testing populations with low disease prevalence.
Methods
A neutralization assay was validated in a set of PCR confirmed positive specimens and in a negative cohort. 9,530 specimens were screened using the Diazyme SARS-CoV-2 IgG serology assay and all positive results (N=164) were reanalyzed using the neutralization assay, the Roche total immunoglobin assay, and the Abbott IgG assay. The relationship between the magnitude of a positive SARS-CoV-2 serology result and the levels of neutralizing antibodies detected was correlated. Neutralizing antibody titers (ID50) were also longitudinally monitored in SARS-CoV-2 PCR confirmed patients.
Results
The SARS-CoV-2 neutralization assay had a PPA of 96.6% with a SARS-CoV-2 PCR test and a NPA of 98.0% across 100 negative controls. ID50 neutralization titers positively correlated with all three clinical serology platforms. Longitudinal monitoring of hospitalized PCR confirmed COVID-19 patients demonstrates they made high neutralization titers against SARS-CoV-2. PPA between the Diazyme IgG assay alone and the neutralization assay was 50.6%, while combining the Diazyme IgG assay with either the Roche or Abbott platforms increased the PPA to 79.2% and 78.4%, respectively.
Conclusions
For the first time, we demonstrate that three widely available clinical serology assays positively correlate with SARS-CoV-2 neutralization activity observed in COVID-19 patients. When a two-platform screen and confirm approach was used for SARS-CoV-2 serology, nearly 80% of two-platform positive specimens had neutralization titers (ID50 >50).
Summary
Clinical performance of a SARS-CoV-2 neutralization assay was evaluated using SARS-CoV-2 PCR confirmed patients and SARS-CoV-2 negative individuals. The neutralization assay was compared with results from SARS-CoV-2 positive serology specimens. We demonstrate that positive SARS-CoV-2 serology results correlate with the presence of neutralization activity against SARS-CoV-2. We show a high false positive rate when using a single SARS-CoV-2 serology platform to screen populations with low disease prevalence; and confirm that using a two-platform approach for COVID-19 seropositives greatly improves positive predictive value for neutralization.
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