Risk factors for persisting measles susceptibility: a case-control study among unvaccinated orthodox Protestants.

Measles is an infectious disease providing lifelong immunity. Epidemics periodically occur among unvaccinated orthodox Protestants in the Netherlands. During the 2013/2014 epidemic, 17% of the reported patients was over 14 years old. Apparently, they did not catch measles during the previous 1999/2000 epidemic and remained susceptible. We wanted to identify risk factors for this so-called persisting measles susceptibility, and thus risk factors for acquiring measles at older age with increased risk of complications