Vaccine 19 (2001) 3097–3103 Age-specific seroprevalence to varicella-zoster virus: study in Swiss children and analysis of European data Christoph Aebi a,b, *, Katharina Fischer a , Meri Gorgievski b , Lukas Matter b , Kathrin Mu ¨ hlemann b a Department of Pediatrics, Uniersity of Bern, CH-3010 Inselspital, 3010 Bern, Switzerland b Institute for Medical Microbiology, Uniersity of Bern, CH-3010 Bern, Switzerland Received 13 April 2000; received in revised form 8 January 2001; accepted 15 January 2001 Abstract 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 ( 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. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Varicella-zoster virus; Seroprevalence; Vaccine www.elsevier.com/locate/vaccine 1. Introduction Varicella is caused by primary infection with the Varicella-zoster virus (VZV). Usually a benign illness, varicella can cause complications both in previously healthy and in immunocompromised individuals. In temperate climates, hospitalization rates for complica- tions vary between 9 and 55 per 10 4 cases among individuals less than 16 years of age [1–3]. Morbidity and mortality are higher among infants and adults [1–4]. Pregnancy is a period of particular risks because primary infection during the first 20 weeks of gestation causes varicella embryopathy in 2% of cases [5] and because varicella in the third trimester is associated with increased severity [6]. Varicella and its complications may be prevented by active immunization using the live-attenuated varicella vaccine [7]. Universal immunization was implemented in the USA in 1995 [8] based on the observation that 80% of hospitalizations for complications of varicella occur in previously healthy children [9] and cannot be prevented by vaccination of risk groups. In contrast, no European country has adopted an immunization strat- egy for varicella as of today. The potential benefits of universal immunization in Europe may be estimated by: (1) the effectiveness of the vaccine; (2) the frequency and severity of complications of varicella; (3) the incidence of varicella in adults; and (4) considerations of cost-effectiveness [10 – 12]. Popula- tion-based data on complications of varicella are scant. We recently reported that in the Canton of Bern, Switzerland, complications necessitating hospitalization in children were 2–5 times less frequent than in North America [3]. However, a report from Britain [13] sig- nalled an upward shift of the age at primary varicella * Corresponding author. Tel.: +41-31-6329487; fax: +41-31- 6329468. E-mail address: christoph.aebi@insel.ch (C. Aebi). 0264-410X/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S0264-410X(01)00035-4