PREVIOUS reports in this series of papers were concerned with the preparation and properties of live attenuated measles virus and the clinical, antigenic and prophylactic effects of the vaccine. The present study was a controlled trial of the clinical, antigenic and prophylactic effects of measles vaccine (attenuated) in institutionalized children.Study SiteThe study was conducted in Building 16 of the Willowbrook State School, an institution for mentally defective children, Staten Island, New York. This H-formed building consisted of four wards, all on one floor, each with a capacity of 50 cribs or beds. Children in Wards A and B . . .