UCSF

Background

Breakthrough cases of SARS-CoV-2 infection correlate with decreased antibody immunity following mRNA vaccination. Measuring kinetics of vaccine efficacy using traditional laboratory approaches is more expensive and can be impractical. In this study, we evaluated the diagnostic performance of a validated COVID-19 point-of-care lateral flow assay (LFA) kit in detecting post-vaccination antibody response.

Methods

We conducted a prospective cohort study of whole blood and plasma samples to evaluate the performance of a LFA in detecting SARS-CoV-2-specific antibodies following mRNA vaccination compared to enzyme-linked immunosorbent assays (ELISAs). Health care workers at 2 tertiary centers who completed an initial BNT162b2 (n = 103) or mRNA-1273 (n = 35) vaccine series were enrolled between June and August of 2021. We performed an exploratory analysis to correlate band strength and antibody concentration of LFAs and ELISAs respectively.

Results

When compared to the ELISA, LFA results showed similar test positivity for plasma samples (P = 0.55), but not for whole blood samples (P < 0.001). For whole blood samples on the LFA, antibody detection differed between BNT162b2 (68.9%, 95% CI: 59.1%-77.7%) and mRNA-1273 (100%, 95% CI: 90.0%-100%, P < 0.001) vaccines. Higher plasma antibody concentrations correlated with greater LFA sensitivity. Samples with thick LFA bands had higher antibody concentrations compared to samples having faint LFA bands (81.8 arbitrary unit [AU]/mL vs. 57.1 AU/mL, P < 0.01).

Conclusions

The performance of a LFA in detecting SARS-CoV-2 antibodies was significantly better when plasma samples were used. The strength of label bands on the LFA may correlate with antibody concentration and could be a useful point-of-care monitoring tool for post-vaccine antibody status.