Seroprevalence of varicella in the French population

Objectives: To assess the age-specific seroprevalence of varicella in the French population and to explore age-adjusted differences according to gender and geographic region. Methods: Data were obtained from 1257 randomly selected, frozen serum samples, from subjects 1 - 30 years of age, that were sent to the Pasteur-Cerba laboratory in November 2003 to January 2004 for the following clinical indications: allergies, respiratory infections, herpes virus infections excluding varicella and endocrinologic tests. IgG concentrations were tested with an indirect enzyme immunoassay. Statistical analyses included use of locally weighted, scatterplot smoothers. Results: Age-specific seroprevalence of varicella increased by > 6-fold between 1 and 8 years of age, ie, from 15.0% (95% confidence interval, 8.6 - 23.5%) for subjects 1 - 2 years of age to 89.0% (95% confidence interval, 81.0 - 94.3%) for those 7 - 8 years of age. The smoothed curve of age-specific seroprevalence suggested that the steepest rate of increase occurred between I and 8 years of age, followed by a considerable slowing in the rate of increase, reaching a prevalence of similar to 95% by age 30. Varicella seroprevalence rates were similar for the samples referred for the 4 clinical indications, as follows: allergies, 76.2%; respiratory infections, 74.0%; herpes virus infections excluding varicella, 73.3%; endocrinologic tests, 73.7% (P = 0.84). Conclusions: Most varicella-zoster virus infections occur during early childhood. Seroprevalence rates reach similar to 50% by 4 years of age and similar to 90% by 8 years. Therefore, the best strategy to reduce the prevalence of wild-type varicella-zoster virus in the French population would be to immunize children 12 - 18 months of age, as is currently performed in the United States.