LAUSR

OBJECTIVE Detecting neutralizing antibodies targeting receptor-binding domain (RBD) is important for the assessment of humoral protection and vaccine efficacy after vaccination. We compared the performance of three surrogate immunoassays for detection of neutralizing antibodies targeting RBD. METHODS We analyzed 115 serum samples obtained from individuals with Ad5-vectored COVID-19 vaccination using two competitive enzyme-linked immunosorbent assays (Wantai BioPharm and Synthgene Medical Technology) and one competitive chemiluminescence assay (YHLO Biotech). Performance evaluation and methodology comparison were performed according to the Clinical and Laboratory Standards Institute related guidelines. RESULTS The precision met the manufacturers' statements. The linear range of the WANTAI was 0.0625-0.545 U/ml and the YHLO was 0.260-242.4 U/ml. The WANTAI's limit of blank (LoB) and limit of detection (LoD) were 0.03 and 0.06 U/ml, respectively. The YHLO's LoB and LoD were 0.048 and 0.211 U/ml, respectively. The correlations of semi-quantitative results of Synthgene with quantitative results of YHLO (ρ = 0.566) and WANTAI (ρ = 0.512) were medium. For YHLO and WANTAI, there was a good agreement (0.62) and a strong correlation (ρ = 0.931). Passing-Bablok analysis and Bland-Altman plot showed a positive bias (112.3%) of the YHLO compared to the WANTAI. The exclusion of samples >50 U/ml did not decrease bias. CONCLUSION These findings contribute to a deeper understanding of surrogate viral neutralization assays and provide useful data for future comparison studies.