Almost 10% of the Italian population is susceptible to measles—namely, they lack immunity either from vaccination or previous infection. Young adults aged 20 to 40 are particularly at risk in many regions, including those with high childhood vaccination coverage. These are the findings of a study led by the Istituto Superiore di Sanità (ISS ) and Fondazione Bruno Kessler and published in the journal The Lancet Infectious Diseases.