This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax email@example.com with numerous contributions by others.
Diptheria is a contagious disease affecting the nose, throat, and
skin. Complications include paralysis (about 20% of patients) and
heart damage (about 50%) (Pantell, Fries, and Vickery). The Merck
manual has a very long list of complications, mostly involving the
heart, and says that complications are likely if antitoxin isn't
administered properly. The death rate was 35% before antitoxin was
available, and is now 10% (Harrison).