Measles serological survey in the Italian population: interpretation of results using mixture model.

In 2003-2004, a national measles seroprevalence study was conducted in Italy and data were analysed by using both commercial ELISA cut-off, and by applying a mixture model. Results of the two methods were compared and interpreted in the light of measles incidence, vaccination coverage and previous seroprevalence data. Seroprevalence rates observed in 2004 were similar to those observed in a previous study conducted in 1996 for children up to 9 years of age, while they were significantly lower in individuals aged 10-19 years. Mixture model approach allowed to better understand these results, suggesting that in these latter age groups there was a waning of vaccine-induced immunity mainly in Northern-Central regions which historically had the highest vaccination coverage.