Objective: Eight Italian Regions have begun offering vaccination against varicella to children aged 13-15 months, with a second dose at 5-6 years of age. A serosurvey was conducted to evaluate the impact of extensive vaccination in these "pilot" Regions.
Design: Samples were collected in compliance with current legislation and after the approval of the Ethics Committee. The qualitative and quantitative determination of antibodies (IgG) against varicella was performed using an ELISA assay with high sensitivity and specificity.
Results: 1,470 samples were analyzed. After the decrease of seropositivity associated with the decay of passively acquired antibody titer, there was a progressive increase of seroprevalence in the other age groups. The comparison with what was recorded in two studies conducted with similar assays in the periods 1996/97 and 2003/04, showed a significant increase in seroprevalence following extensive immunization, particularly in the age classes 1 year, 2-4 years and 5-9 years. The proportion of seropositivity in the age classes 1 year and 2-4 years has more than doubled.
Conclusions: Seroepidemiological studies are a useful tool to evaluate the distribution of susceptible individuals in the population. This study highlighted the impact of extensive vaccination against varicella in eight "pilot" Regions.