Did you know that people vaccinated for diphtheria can still carry and spread diphtheria without showing symptoms of an infection?
"There was no statistical difference in the risk of diphtheria infection among those who had a full, expired, inadequate or no previous vaccination for diphtheria ... Diphtheria toxoid ... does not prevent carrier status or stop the spread of the infection. The identification, isolation and treatment of carriers are very important aspects in the control of diphtheria epidemics. "