Comparison of a rapid fluorescence immunochromatographic test with an enzyme-linked immunosorbent assay for measurement of SARS-CoV-2 spike protein antibody neutralizing activity

Highlights

• Immunofluorescence test and ELISA were used to evaluate SARS-CoV-2 neutralizing activity after vaccination.

• Qualitative agreement between the two methods was high (AUC=0.92).

• Quantitative agreement improved when time from vaccination increased (P < 0.0001).

• Quantitative agreement improved in > 50 year age group at 4 months post vaccination (P < 0.0001).

Abstract

Background

SARS-CoV-2 Spike protein Receptor Binding Domain neutralizing antibodies (NAbs-RBD) inhibit the viral binding to angiotensin-converting enzyme 2 (ACE2) receptors. We compared an ELISA and a fluorescence immunochromatography (FIC) method in NAbs-RBD detection after COVID-19 immunization.

Method

Serum samples from healthcare workers (HCWs) vaccinated with BNT162b2 were collected one and four months after the second dose. NAbs-RBD (%) detection was performed using ELISA cPass™ (FDA approved) and FIC n-AbCOVID-19® assays.

Results

Samples from 200 HCWs [median age (IQR): 45(35−53)] were tested with both assays. There was a good qualitative agreement between the two methods [AUC: 0.92(95%C.I.: 0.89–0.94, P-value:0.007)]. NAbs-RBD (%), one and four months after immunization, were significantly lower with FIC compared to ELISA for all age groups (P-value<0.0001). The quantitative comparison between FIC and ELISA detected slight agreement one month after the second dose [(Lin’s Concordance Correlation Coefficient (CCC): 0.21(95%CI: 0.15–0.27)] which improved four months after the second dose [CCC: 0.6(95%CI: 0.54–0.66)].

Conclusion

FIC had good qualitative agreement with ELISA in the detection of positive NAbs-RBD (%) and could be an alternative for rapid NAbs-RBD (%) testing.