IOM: Serious Adverse Events Rare With Vaccines

Extensive Review Finds Few Causal Relationships

September 12, 2011 08:05 pm David Mitchell

An Institute of Medicine, or IOM, comprehensive review of evidence regarding vaccines and adverse events is providing family physicians with one more resource they can use to reassure parents about the safety of vaccines. The review is the work of an IOM committee that examined more than 1,000 peer-reviewed articles and weighed both epidemiologic and clinical evidence before reaching conclusions about whether a vaccine could cause a specific adverse event.

[Stock photo of scattered empty syringes]

"What they said could be summed up in three brief statements," said Doug Campos-Outcalt, M.D., M.P.A., chair of the department of family and community medicine at the University of Arizona College of Medicine, Phoenix, and a member of the CDC's Advisory Committee on Immunization Practices. "Vaccines are one of the most effective public health interventions of all time. We give hundreds of millions of doses of vaccines. Severe adverse reactions are extremely rare."

Campos-Outcalt said the report is an excellent source of information for family physicians. Although he acknowledged that the 667-page report( is "not good bedtime reading" for the average patient, a free six-page report brief( is available. The IOM also has released a one-page table( that summarizes the level of evidence related to a potential adverse event and a specific vaccine.

Story highlights

  • The Institute of Medicine, or IOM, has released a review of evidence regarding vaccines and adverse events.
  • The IOM committee found that evidence refuted purported links between the measles, mumps and rubella vaccine and both autism and type 1 diabetes.
  • The committee also found that most serious adverse events were rare and often involved patients with compromised immune systems.

"It's another completely neutral group that took a look at this and came to a set of conclusions that can be very reassuring to parents and physicians alike," Campos-Outcalt told AAFP News Now.

The Health Resources and Services Administration, the HHS agency that administers the National Vaccine Injury Compensation Program, requested the review. It marks the third time the IOM has reviewed adverse events since the compensation program was created by Congress in 1986 and the first time since 1994.

Committee chair Ellen Wright Clayton, M.D., J.D., professor of pediatrics and law, and director of the Center for Biomedical Ethics and Society at Vanderbilt University, called the report "the best analysis that's ever been done about potential adverse events" during an Aug. 25 media briefing.

"We have a lot of evidence that vaccines save lives and avert a lot of suffering," she said. "The side effects that we're talking about are relatively rare because it's hard to find them in the general population. The majority of them are short term or readily treated."

An IOM committee reviewed adverse event reports related to vaccines for hepatitis A; hepatitis B; human papillomavirus, or HPV; influenza; measles, mumps and rubella, or MMR; meningococcal disease; tetanus; and varicella. Based on the evidence, the committee assigned 158 vaccine and adverse event relationships to one of the following categories:

  • evidence convincingly supports causal relationship;
  • evidence favors acceptance of causal relationship;
  • evidence favors rejection of causal relationship; and
  • evidence is inadequate to accept or reject causal relationship.

More than 100 of the vaccine and adverse event pairings fell into the category of inadequate evidence. The committee said in its report brief that, in many cases, the adverse event in question was so rare it was difficult to study.

The committee said evidence favored rejection of five vaccine and adverse event relationships:

  • MMR vaccine and autism;
  • MMR vaccine and type 1 diabetes;
  • diphtheria and tetanus toxoids and acellular pertussis, or DTaP, 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.

The purported link between MMR vaccine and autism already has been widely discredited. Last year, The Lancet retracted the 1998 study that initially linked autism to the vaccine.

The CDC said Sept. 2 that there have been 198 cases and 15 confirmed outbreaks( of measles this year in the United States, the highest number since 1996. Ninety percent of the cases were associated with U.S. residents traveling internationally.

The IOM committee, however, did find convincing evidence of a causal relationship between MMR and other side effects, including measles inclusion body encephalitis, which in rare cases can affect people with compromised immune systems, and febrile seizures.

MMR also was one of six types of vaccines -- the others were varicella zoster, influenza, hepatitis B, meningococcal, and tetanus-containing vaccines -- linked to anaphylaxis.

Several other vaccines and adverse events also fell into the category that found convincing evidence to support causal relationships. For example, varicella zoster vaccine is linked to four adverse events due to infection from the vaccine virus strain, including disseminated varicella infection shortly after vaccination and disseminated varicella infection with subsequent infection resulting in pneumonia, meningitis or hepatitis in individuals with immunodeficiencies.

The committee also found convincing evidence of a causal relationship between injection of vaccines, regardless of the antigen involved, and syncope and deltoid bursitis.

Four vaccine and adverse event relationships fell into the category of having evidence that favors acceptance of a causal relationship, which means the committee found strong, but not convincing, evidence:

  • HPV vaccine and anaphylaxis;
  • MMR vaccine and transient arthralgia in female adults;
  • MMR vaccine and transient arthralgia in children; and
  • certain trivalent inactivated influenza vaccines used in Canada in some recent years and a mild and temporary oculorespiratory syndrome, which is characterized by conjunctivitis, facial swelling and upper respiratory symptoms.

"The more serious adverse events we identified we often only saw in case reports," committee member Claiborne Johnston, M.D., Ph.D., associate vice chancellor of research and director of the Clinical and Translational Science Institute at the University of California, San Francisco, said during the media briefing. "We didn't see any epidemiologic evidence to suggest those were occurring with any real frequency in the general population. We're talking about millions of vaccines and only a few case reports of serious events."