Diphtheria is a serious disease that can cause death through airway obstruction, heart failure, paralysis of the muscles used for swallowing and pneumonia. It is caused by the bacterium Corynebacterium diphtheriae, which produces toxins that cause cell death both at the site of infection and elsewhere in the body.

Diphtheria usually begins with a sore throat, slight fever, and swollen neck. Most commonly, bacteria multiply in the throat, where a grayish membrane forms. This membrane can choke the person—the source of its common name in the late 19th century as the “strangling angel.”

Sometimes, the membrane forms in the nose, on the skin, or other parts of the body. The bacteria also release a toxin that spreads through the bloodstream that may cause muscle paralysis, heart and kidney failure, and death.

Approximately 5% of people who develop diphtheria (500 out of every 10,000) die from the disease and many more suffer permanent damage.

“Baby” Ruth Cleveland, first child of President and Mrs. Grover Cleveland died of diphtheria in 1904, at the age of 12. In the 1920s, before the diphtheria vaccine, there were 100,000 to 200,000 reported cases in the USA each year. For example, in 1921 there were 206,000 cases of diphtheria and 15,520 diphtheria-caused deaths, mostly among children.

Early in the 20th century, diphtheria antitoxin became a powerful new tool for the prevention of diphtheria. Unfortunately, there was no oversight as to how it was produced and used, which led to the great tragedy of the St. Louis, Missouri, diphtheria epidemic in 1901. Equine diphtheria antiserum—made from a horse that had died from tetanus—was given to children, causing fatal tetanus. Also, that year there were cases of tetanus among recipients of contaminated smallpox vaccine in Camden, New Jersey. These outbreaks led Congress to enact the Biologics Control Act of 1902, the predecessor to the Centers for Biologics Evaluation and Research of the US Food and Drug Administration, the beginning of vaccine regulatory control.

Active immunization employing diphtheria toxin and antiserum (so-called TaT) was effective but also associated with many adverse events, such as “serum sickness.” However, in the early 1920s it was shown that toxin treated with heat and formalin lost its toxicity but was immunogenic. The production of diphtheria toxoid has evolved since then, but the process remains highly effective in providing protection against disease. However, the fully immunized person who is exposed to the bacterium can, in rare circumstances, still be infected as a “carrier” who usually only develops a mild case, or may not get sick at all. But if they are not fully vaccinated, the risk of getting severely ill after exposure is 30 times higher.

Because of the high level of immunizations now in the USA, only one case of diphtheria (or fewer) occurs each year. However, in areas where the immunization rate has fallen (such as Eastern Europe and the Russian Federation in the 1990s), tens of thousands of people suffered from diphtheria. Even though we do not see many cases, the potential for diphtheria to reemerge is real.