Prevalence of anti-varicella-zoster virus antibodies in French infants under 15 months of age.

Varicella is a widespread disease of childhood resulting from primary infection with varicella-zoster virus (VZV). The objective of this study was to determine the kinetics of the decline of maternal anti-VZV antibodies in French infants between birth and the age of 15 months in order to estimate the duration of passively acquired maternal anti-VZV immunoglobulin G (IgG). This prospective multicenter study was conducted between October 2005 and January 2007 in the pediatric wards and/or pediatric emergency units of seven French hospitals scattered throughout the country. The level of anti-VZV IgG antibodies in serum was measured by a time-resolved fluorescence immunoassay (TRFIA) (the threshold considered positive is 150 mIU/ml). A total of 345 infants were included. Seventy-seven percent of mothers reported a history of varicella. A rapid decline in the prevalence of anti-VZV antibodies was observed during the first few months of life, with the mean antibody titer decreasing from 536 mIU/ml at birth and through 1 month to below the 150-mIU/ml threshold at 3 to 4 months. The half-life of passively acquired maternal immunoglobulins was around 6 weeks. Based on a large number of subjects, this study clearly demonstrated, for the first time in France, high levels of passively acquired maternal antibodies during the neonatal period, and it allowed us to estimate the duration of passively acquired maternal anti-VZV IgG in French infants. After 4 to 5 months, infants had very low levels of maternal anti-VZV IgG, below the 150-mIU/ml cutoff of the VZV IgG TRFIA.