Performance of Three SARS-CoV-2 Immunoassays, Three Rapid Lateral Flow Tests, and a Novel Bead-Based Affinity Surrogate Test for the Detection of SARS-CoV-2 Antibodies in Human Serum

Abstract

For the control of immunity in COVID-19 survivors and vaccinated subjects, there is an urgent need for reliable and rapid serological assays. Based on samples from 63 COVID-19 survivors up to 7 months after symptom onset, and on 50 serum samples taken before the beginning of the pandemic, we compared the performances of three commercial immunoassays for the detection of SARS-CoV-2 IgA and IgG antibodies (Euroimmun SARS-COV-2 IgA/IgG, Mikrogen recomWell SARS-CoV-2 IgA/IgG, and Serion ELISA agile SARS-CoV-2 IgA/IgG) and three rapid lateral flow (immunochromatographic) tests (Abbott PanBio COVID-19 IgG/IgM, Nadal COVID-19 IgG/IgM, and Cleartest Corona 2019-nCOV IgG/IgM) with a 50% plaque-reduction neutralization test (PRNT50) representing the gold standard. Fifty-seven out of 63 PCR-confirmed COVID-19 patients (90%) showed neutralizing antibodies. The sensitivity of the seven assays ranged from 7.0% to 98.3%, and the specificity ranged from 86.0% to 100.0%. Only one commercial immunoassay showed a sensitivity and specificity of greater than 98%.

Keywords: COVID-19; ELISA; SARS-CoV-2; flow cytometry bead-based surrogate test; lateral flow assay; plaque-reduction neutralization test.

FIG 1

Participants’ demographics (n = 63).

FIG 2

Distribution of the PRNT50 titers of the included patients (n = 63). PRNT50, 50% plaque-reduction neutralization test. Method described in Materials and Methods. PRNT50 values of <20 were considered negative.

FIG 3

Results of the ELISAs plotted against the titers from the neutralization assay (n = 63). Values above the maximum or below the minimum in a test were plotted at this maximum or minimum value, respectively (Mikrogen IgA, >150.12 U/ml; Mikrogen IgG, >133.93 U/ml; Euroimmun IgA, >8.54; Serion IgA, <5.0 U/ml; Serion IgG, <3.0 U/ml and >250.0 U/ml). Mikrogen, Mikrogen recomWell SARS-CoV-2 IgA/IgG (Mikrogen, Neuried, Germany), based on the nucleocapsid; Euroimmun, Euroimmun SARS-COV-2 IgA/IgG (Euroimmun, Lübeck, Germany), based on S1 antigen; Serion, Serion ELISA agile SARS-CoV-2 IgA/IgG (Institut Virion/Serion, Wuerzburg, Germany), based on the S1/S2 ectodomain and the nucleocapsid (IgA) or S1/S2 ectodomain antigen (IgG); PRNT50, 50% plaque-reduction neutralization test. Method described in Materials and Methods. PRNT50 values of <20 were considered negative.

FIG 4

Correlation of the PRNT50 titers and the time (in days) between first positive PCR and serum sampling of the included patients (n = 63). PRNT50, 50% plaque-reduction neutralization test. Method described in Materials and Methods. PRNT50 values of <20 were considered negative and plotted as 6 for drawing the logarithmic correlation line. A PRNT50 value of ≥4,860 was plotted as 4,860 for drawing the logarithmic correlation line.