Seroprevalence of Varicella-Zoster virus IgG antibodies in Swiss children during the first 16 months of age

QUESTION UNDER STUDY: To investigate the persistence of maternal IgG antibodies against Varicella-Zoster virus (VZV) in infants and young children. METHODS: Serum specimens of children aged 0-16 months who had been hospitalized in our institution between 1994 and 1999 were identified from our routine serum collection. Exclusion criteria were: preterm delivery (>37 gestational weeks); suspected varicella infection or presence of exanthema of unknown etiology at time of serum collection; transfusion of blood products during 6 months preceding serum collection; foreign born mother; and previous VZV immunization. Serotesting for IgG antibodies against VZV was performed by use of a commercially available ELISA kit. RESULTS: Two hundred and fifty three serum specimens from 240 patients were analyzed. Age distribution of patients at time of specimen collection was: 0-3 months: n=57; <3-6 months: n=47; <6-9 months: n=47; <9-12 months: n=48; <12-16 months: n=54. Seroprevalence rates for IgG antibodies against VZV in the different age groups were 90% (0-3 months), 38% (<3-6 months); 0% (<6-9 and <9-12 months); and 7% (<12-16 months). CONCLUSIONS: Our results demonstrate high levels of passively acquired humoral immunity against varicella in Swiss infants during the first 3 months of life. Beyond the first 3 months of life IgG antibodies against VZV are lacking in the majority of patients and between 6 and 12 months of age all specimens tested were negative. Beyond the first year of life antibodies against varicella were detected in four samples, probably due to previous VZV infection. In accordance with current recommendations, VZV vaccination should ideally be administered to children 9 months of age and older, although our data indicate that successful immunization may be possible at earlier age (6 months onwards) in certain circumstances.