Immunization Issues

Multiple Immunizations and Immune Dysfunction

Updated: Abril 21, 2004

By two years of age, healthy infants in the United States can receive up to 20 vaccinations to protect against 11 diseases.

In view of that, concerns had been raised that too many immunizations could overwhelm an infant’s immune system.

However, in 2002, the Institute of Medicine (IOM) reviewed all available information and determined that the numerous immunizations that children receive do not increase the risk for immune dysfunction.

Specifically, the IOM’s Immunization Safety Review Committee looked at potential biological mechanisms and at epidemiological evidence for or against causality related to risk for infections, the autoimmune disease type 1 diabetes, and allergic disorders.

The committee concluded that receiving numerous vaccines does not cause disease (for example, diabetes) or increase the chance that children get serious infections (for example, ear infections, pneumonia, or meningitis).

The report from the committee stated that “for allergic disease and type 1 diabetes, the evidence from animal and clinical studies is weak that relevant biological mechanisms operate in humans after receipt of vaccines. The biological mechanisms evidence regarding increased risk for infections is strong. However, the committee found that the epidemiological evidence (i.e., from studies of vaccine-exposed populations and their control groups) favors rejection of a causal relationship between multiple immunizations and increased risk for infections and for type 1 diabetes. The epidemiological evidence regarding risk for allergic disease, particularly asthma, was inadequate to accept or reject a causal relationship.”

Read the full report at

An additional study since the report adds support to this conclusion.

Do vaccines weaken the immune system?

Vaccines strengthen, not weaken, the immune system. This is true even for newborn infants. On the other hand, a natural infection clearly can weaken a child’s immune system, making it harder to resist a second infection. For example, a previously healthy child with chickenpox (varicella) may become infected with dangerous bacteria, resulting in an infection severe enough to require hospitalization or even cause death. Similarly, a child with measles infection is more likely to develop middle ear infections or pneumonia if exposed to these bacteria.

Do vaccines “use up” or overload the immune system in infants or children?

No. Infants and children are bombarded with germs every day in the air they breathe and the food they eat, but their immune systems are able to handle these exposures. Vaccination does not overburden a child’s immune system; rather, it strengthens even the young infant’s developing immune system.

The vaccines that are recommended for all children use only a small portion of the immune system’s “memory.” In fact, an additional study since the report adds support to this conclusion. Scientists estimated that based on the immune system’s capacity to respond, a child could theoretically get 10,000 vaccines in one day and still not “use up” his or her immune response or ability to respond.

The same study found that although more vaccines are recommended for children today than in the past, children are actually exposed to fewer antigens (the substances that produce an immune response) in vaccines than ever before due to advances in chemistry and vaccine production technology.