significance of this issue, the disease burden (e.g., seriousness, treatment, complications) associated with autoimmune and allergic diseases, especially type 1 diabetes and asthma, is reviewed here. Also discussed are indications of public concern about the safety of multiple immunizations and ideas that have been put forward about alternative approaches to the formulation of immunization policy.

Disease Burden

Autoimmune Disorders: Type 1 Diabetes

As noted, diseases of autoimmunity affect 3 to 5 percent of the U.S. population (Jacobson et al., 1997), which translates into as many as 14 million people in 2001. From 500,000 to 1,000,000 people in the United States are thought to have type 1 diabetes, based on estimates that this form of the disease accounts for 5 to 10 percent of the roughly 10 million diagnosed diabetes cases (NIH, 1999). No national surveillance system exists to provide data on the incidence of type 1 diabetes. Rates from local diabetes registries and research projects suggest that about 30,000 new cases develop each year in the United States (LaPorte et al., 1995). Internationally, various registries indicate an average incidence increase of 3% per year (Onkamo et al., 1999). The disease can develop at any age, but incidence rates are higher in children and young adults. Moreover, among children under age 16, the incidence of type 1 diabetes is higher than that of other chronic illnesses, including all forms of cancer combined (Libman et al., 1993).

In type 1 diabetes, the destruction of insulin-producing beta cells in the pancreas prevents proper metabolism of glucose. If not treated, the disease is fatal. Administration of insulin one or more times each day helps compensate for the loss of the beta cells, but the dosage must be calibrated to account for food intake and exercise levels. Children and adults with type 1 diabetes must monitor their blood sugar levels regularly. If blood sugar is not maintained at appropriate levels, there is risk of acute complications, particularly coma. Ketoacidotic coma occurs if insulin administration is inadequate, resulting in hyperglycemia and ketone production. Hypoglycemic coma results if insulin administration is excessive for the blood glucose level.

Type 1 diabetes is associated with many serious long-term complications (Harris, 1995). Mortality rates are elevated at all ages, especially for women and girls, and life expectancy may be reduced by as much as 15 years. Acute coma is the greatest mortality risk during the first years with the disease, replaced over time by renal disease. Among persons who have had Type 1 diabetes for 30 years or more, cardiovascular disease accounts for most deaths. Several chronic complications are also common, and they are more likely to occur if blood sugar levels are poorly controlled. One such complication, diabetic retinopathy, is a leading cause of blindness in the United States. People with diabetes are also at risk of kidney damage that can progress to end-stage renal disease. Neuropathies



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