Age-specific seroprevalence to varicella-zoster virus: study in Swiss children and analysis of European data.

Up to date epidemiological data provide the rationale for potential varicella immunization strategies in Europe. The scope of this study was: (1) to generate new seroprevalence data by evaluating sera of 970 individuals aged 0-16 years for the presence of IgG against Varicella-zoster virus (VZV); and (2) to review existing seroprevalence data. Of 256 individuals >12 years of age, 96.1% (95% confidence interval [CI], 93.7-98.5) were seropositive. Swiss citizens > 12 years of age were less likely to be seronegative than foreign citizens (2.3 vs. 15.4%; odds ratio, 0.17; CI, 0.05-0.58). The age-specific seroprevalence curve demonstrated a peak at 7 years of age (84.9%; CI, 75.2-94.5) followed by lower rates at 8 and 9 years. A peak at 7-10 years of age was found in all previously reported seroprevalence curves (chi(2)-test for trend of pooled data, P = 0.09; Poisson analysis, P < 0.001). It is concluded that: (1) > 90% of individuals in Europe acquire immunity against VZV before adolescence; (2) there is no evidence for a recent upward shift of the age at primary varicella; and (3) there may be a north-to-south gradient of seroprevalence. The peak at 7-10 years may represent a transient loss of detectable antibody by some individuals.