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Serology and Neutralization Assays for COVID-19


The global response to COVID-19 is leading to rapid advances in diagnostic, surveillance, and vaccine and therapeutic development. A critical measurement underpinning much of these efforts is a serological assay that helps to assess the complex patient responses to SARS-CoV-2. Specifically, reliable and rapid serological testing is needed to monitor the spread of the virus, patient immunity against the virus, and to determine the efficacy of vaccines and therapeutics. Yet, serology test results are highly variable for existing serologic tests, in part due to the lack of well characterized globally traceable reference materials needed for validation and assay control.  Leveraging our Flow Cytometry Quantitation Consortium and state-of-the-art facilities, we have developed a rapid, multiplexed, and sensitive flow cytometry-based serological assay as well as a BSL-3 sparing neutralization assays (surrogate bead-based neutralization assay and pseudo-virus neutralization assays).  

This work has supported the development of

  • WHO/BS.2020.2403 WHO International Standard and Reference Panel for anti-SARS-CoV-2 antibody
  • WHO/BS/2022.2427: 2nd WHO International Standard for anti-SARS-CoV-2 immunoglobulin and Reference Panel for antibodies to SARS-CoV-2 variants of concern
  • Human SARS-CoV-2 Serology Standard developed by NIH/NCI Serology Science Network (SeroNet) and FNLCR.

These assays also enable the development of a robust measurement infrastructure for serological assays and associated critical reagents. 



Multiplexed bead-based SARS-CoV-2 serological assay

We have developed a validated multiplexed bead-based SARS-CoV-2 serological assay that measures different antibodies produced by a patient (IgG, IgM, IgA). In collaboration with the NIST Applied and Computational Mathematics Division, we have developed a new strategy to classify more confidently the positive and negative samples. The validated assay was used to characterize the first and second WHO Serology Reference Panels through inter-laboratory studies as well as the study for the development of the US SARS-CoV-2 serology standard and a large-scale follow-up evaluation study led by NIH/NCI SeroNet and FNLCR.

BSL-3 sparing neutralization assays

We have developed surrogate bead-based neutralization assay via flow cytometry and pseudo-virus neutralization assays via live cell imaging and flow cytometry to assist SARS-CoV-2 vaccine and therapeutic development.  These assays will enable the functional assessment of the ability of serum antibodies to prevent cell binding, entry, or other effects of the virus on the cell in vitro. Data showed excellent correlation between our serology and bead-based neutralization assay results.

Pseudovirus neutralization assay by two analysis methods, fluorescence imaging (left image) and flow cytometry (right plot)
Pseudovirus neutralization assay by two analysis methods, fluorescence imaging (left image) and flow cytometry (right plot) with the percent pseudovirus infected cells expressing green fluorescence protein (GFP) respective to the percent infected cells in the absence of neutralizing antibodies for calculating the percent reduction.

Interlaboratory study and reference materials to enable more quantitative and harmonized serology assays

NIST and CDC are leading an effort to collect data through an interlaboratory study to

  • Determine the suitability of a mAb panel to be used in conjunction with the WHO International Standard to enable more quantitative serology assays
  • Develop a mAb panel to enable comparability and traceability of serological assay results collected over time as new variants emerge
  • Determine suitability of well characterized mAb as reference materials to correlate serological and neutralization assays

Currently, two manuscript reports are in preparation detailing key findings of the inter-laboratory study that exceed the original objectives given above.


Development of a Cell-Based SARS-CoV-2 Pseudovirus Neutralization Assay Using Imaging and Flow Cytometry Analysis

Towards Quantitative and Standardized Serological and Neutralization Assays for COVID-19

Created November 12, 2020, Updated August 10, 2023