Differences were found in the affected age groups among the Roma/Sinti and the rest of population. As expected in a susceptible population, the most affected age group in the Roma/Sinti population was the 1-4 year-old age group. Conversely, in the Italian ethnic population, which had a higher percentage of vaccinated subjects with respect to the Roma/Sinti population, especially among young children, most cases occurred in the 15-19 year-old age-group.