On Dec. 9, 1999, the diphtheria and tetanus toxoids and acellular pertussis vaccine (Tripedia by Connaught) was licensed.

Following the widespread use of tetanus toxoid–containing vaccines, tetanus infections have become an uncommon occurrence in the United States. In 1947, the incidence of reported cases was 0.39 per 100,000 in the United States. This number dropped dramatically, and from 1998 to 2000, the average incidence was approximately 0.16 cases per 1,000,000 representing a 96 percent decrease in the incidence rate