Evaluation of a Commercial Glycoprotein Enzyme-Linked Immunosorbent Assay for Measuring Vaccine Immunity to Varicella

Purpose: To evaluate a recently marketed commercial glycoprotein enzyme-linked immunosorbent assay (gpEIA) kit, the VaccZyme (TM) VZV gpEIA, for measuring the immunity of varicella-vaccinated children. Materials and Methods: We investigated the accuracy and reproducibility of the VaccZyme (TM) VZV gpEIA kit for the detection of antibodies to VZV. We also examined the sensitivity, specificity, and correlation between antibody titers calculated with gpEIA versus fluorescent antibody to membrane antigen (FAMA) by using sera of 349 children, ranging from 1 to 6 years old. Results: VaccZyme (TM) VZV gpEIA gave precise and reproducible intra- and inter-assay results. FAMA and gpEIA titers showed a linear correlation (Pearson correlation coefficient=0.987). The sensitivity and specificity of the VaccZyme (TM) gpEIA was 31.4% and 100%, respectively, when the guidelines of the gpEIA (<100 mIU/mL) and FAMA 1:4 were adopted as cutoff values. However, the maximum sensitivity and specificity were 88.9% and 95.1%, respectively, with the highest correlation (kappa=0.840), if the cutoff values were set with gpEIA at 49.7 mIU/mL and FAMA 1:16. Conclusion: These results demonstrate that the VaccZyme (TM) VZV gpEIA kit gave precise and reproducible data for measuring antibody titer after varicella vaccination. The results also showed that the antibody titer calculated with the VaccZyme (TM) gpEIA kit strongly correlated with the FAMA titer. However, cutoff values should be re-optimized for the evaluation of vaccine immunity.