Mazelen epidemie in De Bilt, 1991

In this report a measles outbreak with a total of 37 patients has been studied in a well vaccinated secondary school in Bilthoven, with 949 students (aged 12-20 years). The vaccination coverage was over 90%. The students were asked to report disease symptoms and vaccination history. On the basis of reported clinical signs suggestive for measles they were selected for further laboratory studies. We were not allowed to include pupils without clinical symptoms as a control group. The majority of patients had been vaccinated with live attenuated measles vaccine after their first birthday. We found that measles infection among vaccinated individuals does not always present with classical symptoms. We do not know the extent of spread of measles virus among the school population without clinical symptoms. Within the school the virus spread was facilitated by the good possibilities for the pupils to mix and regroup between lessons in the central hall and corridors. During the outbreak there was no spread of infection in the population outside the school. Complications of measles have not occurred in this outbreak.