TABLE 1.

Methods used to measure antibodies to VZV

Test	Comments
ELISA	Uses extract from cells infected with VZV as antigen. Many commercial tests available. Lacks good sensitivity and specificity, particularly for measuring antibody titers following vaccination. Can be automated, so is useful to test large numbers of sera.
gpELISA	Uses glycoproteins of VZV as antigen. Not commercially available. Used to evaluate VZV antibodies in many vaccine studies. Many experts consider this test oversensitive. Six-week postvaccination titer inversely correlated with risk of breakthrough varicella; arbitrary cutoff at 5 gpELISA units suggested as correlate of protection.
FAMA	Uses live, unfixed cells infected with VZV as antigen. Not commercially available. High correlation of titers of 1:4 or greater to protection from varicella following close exposure to virus. Used successfully to evaluate immunity in small vaccine studies in healthy and immunocompromised populations.
LA	Uses latex particles coated with VZV glycoproteins as antigen. High correlation between the results of FAMA and LA assays. Requires experience in reading agglutination to interpret the test. Not automated.