Routine childhood immunizations and adult boosters prevent the disease. See: Diphtheria immunization (vaccine)
American Academy of Pediatrics Committee on Infectious Diseases. Recommended immunization schedules for children and adolescents -- United States, 2008. Pediatrics. 2008;121(1):219-220.
Centers for Disease Control and Prevention. Recommended adult immunization schedule---United States, 2009. MMWR. January 9, 2009;57(53);Q1-Q4.
Centers for Disease Control and Prevention. Recommended immunization schedules for persons aged 0 through 18 years---United States, 2009. MMWR. January 2, 2009;57(51&52);Q1-Q4.