Vaccine Safety > Issues of Interest > Multiple Vaccines 
New Institute of Medicine (IOM) Report
Immunization Safety Review: 
Multiple Immunizations and Immune Dysfunction

1. Why was the report done?
2. How does the committee examine a hypothesis?
3. What specific questions did the committee consider in its review of multiple vaccines and immune dysfunction?
4. What important data did the committee review when considering if the recommended immunization schedule can overload an infant’s immune system?
5. What were the committee’s conclusions regarding multiple vaccines and immune dysfunction?
6. Did the committee consider the “hygiene hypothesis” as a possible mechanism by which multiple immunizations can make infants susceptible to immune dysfunction?   
7. What conclusion did the committee make about possible biological mechanisms by which multiple immunizations could possibly influence an individual’s risk for infections?
8. What recommendations did the committee make regarding policy, research, and communication?

Related links/pages:

• Links to actual IOM report

• More information on the Safety of Multiple Vaccinations

1. Why was the report done?

Public confidence in our immunization programs is essential to our nation’s health. In recent years, increasing public attention has focused on issues regarding vaccine safety. Vaccine safety concerns may decrease public acceptance of immunizations and result in resurgence of vaccine-preventable diseases. Issues involving the safety of vaccines, particularly childhood vaccines, may concern certain members of the public, health care professionals, the public health community, the media, Congress, vaccine manufacturers, and federal agencies.

In response to these concerns, the Centers for Disease Control and Prevention and the National Institutes of Health have asked the National Academy of Sciences, Institute of Medicine (IOM) to establish an independent expert committee to review hypotheses about existing and emerging immunization safety concerns. These reviews include an assessment of factors such as the biologic mechanisms of the hypothesis, competing alternative hypotheses, as well as the available scientific evidence to date.

This is the third report completed by the IOM committee. The first report, released in April 2001, examined the hypothesized link between Measles, Mumps, and Rubella (MMR) vaccine and autism; this was followed by a second report in October 2001 concerning the hypothesis that thimerosal-containing vaccines may cause neurodevelopmental disorders. Information about these reports can be obtained at the following Web sites:

• Measles, Mumps, and Rubella (MMR) Vaccine & Autism
  http://www.cdc.gov/nip/news/iom-04-24.htm#reason  
• Thimerosal-containing Vaccines and Neurodevelopmental Disorders http://www.cdc.gov/nip/news/iom-thim10-1-01.htm  
         

2. How does the IOM committee examine a hypothesis?

For each hypothesis to be examined, the committee assesses both the scientific evidence and the issue’s significance in a broader societal context. For this review, the scientific assessment has two parts:

1. an examination of evidence of any biological mechanisms relevant to the hypothesis (these are designated as theoretical only, weak, moderate, or strong) and
2. An examination of the evidence regarding a possible causal relation between the vaccine and the adverse event. 

The significance assessment considers the nature of the health risks associated with the vaccine-preventable disease and with the adverse event in question and other societal concerns. The findings of the scientific and significance assessments provide the basis for the committee’s recommendations.

The Immunization Safety Review Committee is composed of 15 members with expertise in pediatrics, neurology, immunology, internal medicine, infectious diseases, genetics, epidemiology, biostatistics, risk perception and communications, decision analysis, public health, nursing, and ethics. The committee members were selected on the basis of strict criteria to eliminate any potential or perceived conflict of interest. 

3. What specific questions did the committee consider in its review of multiple vaccines and immune dysfunction?

Because immune system dysfunction is a broad term, the committee focused its review on the following questions:

• Do multiple immunizations have short-term effects on developing infants’ immune systems that leave them susceptible to other infections?
• Does exposure to multiple vaccines directly and permanently redirect the immune system toward autoimmunity, as reflected in type 1 diabetes?
• Does exposure to multiple vaccines directly and permanently redirect the immune system toward allergy, as reflected in asthma?

In order to conduct their review, the committee needed to focus on defined conditions like diabetes mellitus and asthma for which studies can be reviewed and compared, as opposed to vaguely defined, atypical or non-specific conditions. 

4. What important data did the committee review when considering if the recommended immunization schedule can overload an infant’s immune system?

Central to concerns about multiple immunizations is whether the recommended immunization schedule overloads an infant’s immune system. This concern seems to be increasing as the number of recommended vaccines increases.  However, the committee reviewed data that indicate that the number of antigens contained in the vaccines that make up the recommended childhood immunization schedule actually has decreased over the past 20 to 30 years, despite the increase in the number of vaccines and vaccine doses. This is due to removal of smallpox and whole cell pertussis vaccines from the childhood immunization schedule. The committee also reviewed estimates that suggest the capacity of the infant immune system is at least 1000 times greater than what is required to respond to immunization.     

This page last modified on February 21, 2002