Ongoing outbreak with well over 4,000 measles cases in Italy from January to end August 2017 - what is making elimination so difficult?

We report an ongoing measles outbreak in Italy, with over 4,400 cases reported in 20 Regions from January to August 2017. Median age was 27 years, 88% of the cases were unvaccinated. The highest incidence was in infants below one year of age and 7% of cases occurred among healthcare workers. Three deaths occurred and two cases of encephalitis were reported. Wide immunity gaps and nosocomial transmission are major challenges to measles elimination in Italy.