Fig. 3. Low-cost Rapid LFA oral fluid test to detect low circulating Abs.

Assess the correlation between blood and oral fluid IgG against (A) Spike and (B) RBD. The nonparametric Spearman correlation coefficients (rs) for the plots are shown. (C) Assess low Luminex RBD binding agreements with the negative LFA oral fluid test. Assess negative LFA oral fluid test agreements with neutralizing titers of (D) Wuhan, (E) Delta, and (F) Omicron strains. The P value summary from the Mann-Whitney nonparametric unpaired test to determine the difference between the groups is shown above the scatterplot. ****P < 0.0001.