Measurement of measles virus-specific neutralizing antibodies: evaluation of the syncytium inhibition assay in comparison with the plaque reduction neutralization test.

Abstract Plaque reduction neutralization (PRN) is the “gold-standard” for the measurement of measles-specific neutralizing antibodies. However, it is a complicated assay and tends to be operator-dependent. It has been suggested that the simpler syncytium inhibition assay (SIA) can give results comparable to the PRN test. We compared these two assays using 594 serum or plasma samples obtained from children at various times after natural infection, primary measles immunization, and measles revaccination. The results of the two assays correlated well overall (r = .86; p 800 are thought to indicate protection against clinical illness and infection respectively. The equivalent SIA cut-off values using 125 plaque-forming units as the challenge inoculum were ≥16 and >128 respectively. At low PRN titers ( p