A Comparative Study of Nine SARS-CoV-2 IgG Lateral Flow Assays Using Both Post-Infection and Post-Vaccination Samples

Abstract

Background: Since the SARS-CoV-2 pandemic, lateral flow assays (LFA) detecting specific antibodies have entered the market in abundance. Despite being CE-IVD-labeled, the antigenic compounds of the assays are often unknown, the performance characteristics provided by the manufacturer are often incomplete, and the samples used to obtain the data are not detailed.

Objective: To perform a comparative evaluation of nine lateral flow assays to detect IgG responses against SARS-CoV-2. For the evaluation, a carefully designed serum panel containing post-infection samples and post-vaccination (both mRNA vaccine and inactivated virus vaccine) samples was used.

Results: The sensitivity of the assays overall ranged from 9 to 90.3% and the specificity ranged from 94.2 to 100%. Spike protein-containing assays performed generally better than the assays with only nucleocapsid protein. The sensitivity of some assays was higher on post-infection samples, while other assays had a higher sensitivity to post-vaccination samples.

Conclusion: A comparative approach in the verification of LFAs with an adequately designed serum panel enabled the identification of the antigens used in the assays. Sensitivities differed between post-infection and post-vaccination samples, depending on the assays used. This demonstrates that the verification of assays must be performed with samples representative of the intended use of the assay.

Keywords: COVID-19; SARS-CoV-2; inactivated virus vaccine; lateral flow assay (LFA); mRNA-vaccine; post-infection; post-vaccination.

Figure 1

Plotted are the semi-quantitative LFA results (x-axis) against the anti-spike IgG response (y-axis). Results are categorized as negative IgG response (NEG), weakly positive IgG response (WPOS), and positive IgG response (POS).

Figure 2

Semiquantitative LFA responses (x-axis) versus anti-spike IgG response (y-axis) sorted by vaccine (Moderna and Pfizer represent mRNA vaccine, SinoVac represents inactivated virus vaccine, and None represents the post-infection cohort). Results are categorized as negative IgG response (NEG), weak positive IgG response (WPOS), and positive IgG response (POS).

Figure 3

(A) Correlation heat map of anti-spike IgG and LFA results sorted by LFA and antigen. Clustering of spike-protein-containing LFAs and exclusively nucleocapsid-containing LFAs can be seen. The LFA from Abnova clusters with the nucleocapsid protein-containing assays. (B) Correlation heat map of anti-spike IgG and LFA results sorted by LFA. The output of the regression models used can be found in the Supplementary Materials.