Seroprevalence of varicella-zoster virus as measured by fluorescent antibody to membrane antigen assay and glycoprotein enzyme-linked immunosorbent assay more than 10 years after initiation of a universal vaccination program: An observational study

Universal varicella vaccination (UVV), as a single dose to children aged 12 to 15 months, was introduced in Korea in 2005. A seroprevalence study is required to upgrade this UVV strategy. The fluorescent antibody to membrane antigen (FAMA) assay is the gold standard for varicella-zoster virus (VZV) immunity testing. However, no standard operating procedure (SOP) has been developed for the FAMA assay, in which either glutaraldehyde or acetone may be used for VZV-infected cell fixation. In this observational study, we aimed to investigate the age-specific seroprevalence in Korean children and adults. Additionally, with glycoprotein enzyme-linked immunosorbent assay (gpELISA) as the reference, we evaluated the performance of the FAMA assay using acetone-fixed cells. Four hundred sera were analyzed using the FAMA assay (acetone-fixed cells) and gpELISA, comprising 50 subjects from each age category. In the FAMA assay, the seropositivity rate decreased from 82.0% in the 1 to 4-year-old group to 58.0% in the 5 to 9-year-old group (95% confidence interval [CI]: 69.2-90.2 and 44.2-70.6, respectively; P = .009), while that in the gpELISA decreased from 80.0% to 52.0% (95% CI: 67.0-88.8 and 38.5-65.2, respectively; P = .003). In both methods, the seropositivity rates ranged from 95% to 100% in the population aged ≥ 20 years. We observed a significant correlation between the 2 methods, with a correlation coefficient of 0.795 (P < .001). In receiver operating characteristic analysis using the gpELISA results as a reference, the area under the curve for the FAMA assay was very high at 0.995 (95% CI: 0.990-1.000; P < .001). Compared to the gpELISA, the sensitivity, specificity, and kappa value of the FAMA assay were 99.4%, 79.3%, and 0.84 (nearly perfect), respectively. The seropositivity rate of the 5 to 9-year-old group indicated waning immunity over time and supported implementation of a second dose in the UVV program. The results of the FAMA assay were comparable to those of the gpELISA. Although further study is needed to standardize procedures, our results suggest that the FAMA assay using acetone-fixed cells can be used widely and can be included in a universal FAMA assay SOP.