An analysis of more than 1,000 research articles concluded that few health problems are caused by or clearly associated with vaccines, but there are some adverse outcomes of note, the Institute of Medicine concluded in a comprehensive 2011 report on the issue.1

A committee of experts convened by the IOM to review the scientific literature on vaccines found evidence of 14 rare outcomes, including seizures, inflammation of the brain, and fainting. The panel also found some data on associations between specific vaccines and allergic reactions and temporary joint pain. The evidence underscored that there are no links between immunization and autism or type 1 diabetes.

The IOM committee reviewed the safety of some commonly used vaccines, including those for varicella zoster, influenza, hepatitis B virus, human papillomavirus, hepatitis A, measles, mumps, rubella (MMR) vaccine, the meningococcal vaccines, and tetanus-containing vaccines that do not carry the whole-cell pertussis component. For the vast majority (135 vaccine-adverse event pairs), the evidence was inadequate to accept or reject a causal relationship. In many cases, the adverse event being examined was an extremely rare condition, making it hard to draw any definitive conclusions, the IOM reported.

The IOM found no evidence of the following five vaccine–adverse event relationships of particular concern:

  • MMR vaccine and autism,
  • MMR vaccine and type 1 diabetes,
  • DTaP (tetanus) vaccine and type 1 diabetes,
  • Inactivated influenza vaccine and Bell’s palsy, and
  • Inactivated influenza vaccine and exacerbation of asthma or reactive airway disease episodes in children and adults.

Pox problem

The IOM committee concluded that the evidence convincingly supports a causal relationship between some vaccines and some adverse events. As a live vaccine, the varicella zoster vaccine is linked to four specific adverse events, all due to infection from the vaccine virus strain:

  • Disseminated varicella infection (widespread chickenpox rash shortly after vaccination);
  • Disseminated varicella infection with subsequent infection resulting in pneumonia, meningitis, or hepatitis in individuals with demonstrated immunodeficiencies;
  • Vaccine strain viral reactivation (appearance of chickenpox rash months to years after vaccination);
  • Vaccine strain viral reactivation with subsequent infection resulting in meningitis or encephalitis (inflammation of the brain).

In addition, less comprehensive evidence indicated a causal relationship for other vaccine–adverse event interactions. In these cases, the evidence is strong and generally suggestive, but not firm enough to be described as convincing, the IOM noted. These include:

  • HPV vaccine and anaphylaxis (allergic reaction);
  • MMR vaccine and transient arthralgia (temporary joint pain) in female adults and children.


  1. IOM. Adverse Effects of Vaccines: Evidence and Causality. August 25, 2011: