Diphtheria was once the leading cause of death among children in the United States. Diphtheria was feared greatly. In the 1920s, 100,000-200,000 cases of diphtheria occurred each year resulting in 13,000-15,000 deaths. Diphtheria is now rare (fewer than five cases reported per year since 1980) thanks to improved living conditions and widespread immunization. However, recent surveys show that up to 60% of adults in the U.S. are not protected against diphtheria.
Protection provided by childhood immunization decreases over time and many adults do not receive recommended booster doses (every 10 years). This is a concern because diphtheria the disease continues to occur in other parts of the world. From 1990 to 1998, more than 150,000 cases and more than 5,000 deaths were reported in the former republics of the Soviet Union. This outbreak, and others around the world, illustrates what can happen when immunity levels fall. Outbreaks in other countries also increase the risk of diphtheria importation into the United States.