Immunity to measles in Italian children and adolescents: a persistent problem in view of measles elimination

BACKGROUND: Despite efforts to increase coverage by two doses of measles vaccine in Italy, measles continues to circulate, with over 13 000 cases of disease since 2013. This study aimed to evaluate immunity to measles in Italian children and adolescents.METHODS: A total of 378 serum samples from subjects aged 9months-18years were collected in Northern, Central and Southern regions of Italy between 2012 and 2016. Specific IgG antibodies against measles were measured by a commercial ELISA kit.RESULTS: The frequency of IgG-positive samples ranged from 10.5% in infants under 1year to 98.3% in children aged 6-7years. The frequency of IgG was 72.2% in subjects aged 1-2years, 85.6% in those aged 3-5years and 88.3 and 86.8% in those aged 8-10 and 11-18years, respectively. In Northern Italy, IgG prevalence was consistent with data on vaccination coverage, whereas some differences were observed in samples from subjects aged more than 8years in Central and Southern Italy.CONCLUSIONS: Our findings confirm that a large proportion of children and adolescents in Italy are still susceptible to measles. While data on first- and second-dose measles vaccination are essential, they are not sufficient to identify susceptible population cohorts to be targeted by vaccination.