To compare the correlation and consistency of fluorescence immunochromatography (FIC) assay and latex immunochromatography (LIC) assay with ELISA, and to evaluate their clinical utility for SARS-CoV-2 antibody monitoring in fully vaccinated populations.

511 serum and plasma samples were collected from vaccinated subjects recruited by Macao University of Science and Technology Hospital. All samples were tested for SARS-CoV-2 antibodies by ELISA, FIC assay and LIC assay, respectively. Negative-positive compliance rate, positive and negative predictive values, and Cohen's Kappa values for inter-assay agreement were calculated.

The performance test results showed that the FIC minimum detection limit was 50 ng/ml with linear detection range was 50~2000 ng/ml, while LIC minimum detection limit was 200 ng/ml. There were no cross reaction with antibodies produced by other respiratory viral and bacterial infections. For serum samples, overall compliance rate for FIC assay and LIC assay was 88.26% and 90.41%, respectively. The Cohen's Kappa values were 0.766 and 0.809, respectively. Plasma samples exhibited higher compliance rate (90.80% for both methods) with Kappa values of 0.816 and 0.817, respectively, indicating significantly stronger compliance and consistency than serum samples. Longitudinal monitoring of vaccinated populations revealed that antibody positivity increased gradually after the first two doses of vaccination (ELISA: 60.38%, FIC: 54.72%, LIC: 69.81%), but declined by 180 days (ELISA: 43.24%, FIC: 53.15%, LIC: 66.67%), and rebounded post-booster to 98.75% across all assays. The plasma and serum antibody patterns were similar.

FIC assay and LIC assay have good agreement with ELISA in detecting antibody levels to SARS-CoV-2, which can quantify neutralizing and total antibody levels in a timely manner, and are both suitable for monitoring immunization levels in large-scale populations.