Early U.S. military immunization against tetanus and diphtheria: historical context and current importance.

Prior to the Second World War, toxoid immunizations for both tetanus and diphtheria had been developed but were not widely used in adults. Starting in 1941, however, the U.S. Army began extensive immunization with tetanus toxoid. Tetanus decreased dramatically, with only 12 tetanus cases (1 case per million) developing during the war, mostly in imperfectly immunized soldiers. Diphtheria immunization was more complicated, as many adults in 1941 had some natural anti-toxic immunity to diphtheria. A decision to not immunize the U.S. military against diphtheria was made due to low prevalence of the disease and high rates of adverse events. During the war, however, unexpectedly high rates of debilitating cutaneous diphtheria were seen in desert and jungle warfare, among prisoners of war, and amid epidemics of respiratory diphtheria in Europe. Those diphtheria cases resulted in the requirement for U.S. soldiers to be immunized starting in 1945. Adjusted toxoid doses post-war eventually arrived at an accepted dual toxoid regimen. Mass immunization remains the best prevention against diphtheria.