It’s a disease that’s spread through person-to-person contact and is caused by a bacterium. It affects the upper respiratory system and can be fatal by blocking airways and can release a toxin that can cause paralysis and heart failure. The vaccine was developed in the 1940s. Before the vaccine, about 100,000 to 200,000 diphtheria cases were reported in the United States. After the vaccine became prevalent, only about one case is reported in the United States each year.