By two years of age, healthy infants in the United States can receive up to 20 vaccinations to protect against 11 diseases. Although most people know that vaccines effectively protect against serious infectious diseases, many parents question: Can too many immunizations overwhelm an infant's immune system? Reasonable theories exist for how vaccines could cause these effects.

The Immunization Safety Review committee reviewed the evidence regarding the hypothesis that multiple immunizations increase the risk for immune dysfunction, with a focus on evidence related to risk for infections, the autoimmune disease type I diabetes, and allergic disorders.

The committee found that evidence favors rejection of a causal relationship between multiple immunizations and increased risk for infections and for type I diabetes. They also found that epidemiological evidence regarding risk for allergic disease, particularly asthma, was inadequate to accept or reject a causal relationship. The committee recommended continued attention in the form of policy analysis, research, and communication strategy development to inform those concerned about these issues and to encourage parents to vaccinate their children.

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