IOM review ties few adverse effects to vaccines

Aug 25, 2011 (CIDRAP News) – An Institute of Medicine (IOM) analysis found few health problems that were clearly linked to eight common vaccines, according to a report released today.

The IOM's analysis of adverse events related to eight vaccines covered in the federal Vaccine Injury Compensation Program (VICP) addressed some of the vaccine and side-effect issues that have been flash points in the clash between the anti-vaccine movement and the science community. For example, the reviewers reiterated the conclusion that the measles, mumps, and rubella (MMR) vaccine does not cause autism.

The report, ordered by the US Department of Health and Human Services, is intended to help people involved in the VICP system, including staff, people filing claims, and special masters in the US Court of Federal Claims who rule on vaccine cases. The court was established in 1986 under the VICP to curb the number of lawsuits against physicians and vaccine makers after a scare involving the diphtheria, tetanus, and pertussis (DTaP) vaccine threatened the national vaccine supply.

Dr. Ellen Wright Clayton, who chaired the IOM committee, said in a media briefing today that vaccines are important tools and that all healthcare interventions carry possible risks. "And vaccines are no exception," said Clayton, who is professor or pediatrics and law and director of the Center for Biomedical Ethics and Society at Vanderbilt University in Nashville.

The group found that few health problems were clearly related to vaccines. Adverse events were rare and involved short-term effects that were readily treated, she said.

The IOM's findings represent the first comprehensive study since 1994 focusing on adverse events and the eight vaccines: varicella zoster, influenza, hepatitis B, human papillomavirus (HPV), tetanus toxoid–containing vaccines other than those containing the whole-cell pertussis component, MMR, hepatitis A, and meningococcal.

During the assessment, which included more than 1,000 research studies, the IOM committee looked at 158 vaccine–adverse event pairs. The group's 667-page report is available on the IOM's Web site.

Clayton emphasized that the group's focus was narrow: to assess findings on potential immunization risks, not to quantify risks or make risk-benefit projections.

Committee members used two types of studies to assess the adverse effects, epidemiological studies to signal if certain adverse effect risks were higher or lower for each vaccine and biomechanical studies to explore how and why certain effects can occur.

They made one of four conclusions for each vaccine–adverse effect pair: convincing evidence, favors acceptance, favors rejections, and inadequate data to accept or reject.

Convincing evidence supported 14 relationships between vaccines and adverse events, according to the report. They included anaphylaxis and six vaccines: MMR, varicella, influenza, hepatitis B, meningococcal, and tetanus toxoid.

They found that the MMR vaccine can trigger seizures in some people and that it can lead to a rare form of brain inflammation in people with severe immune-system deficiencies. In a minority of patients, the varicella vaccine can be linked to conditions such as brain swelling, pneumonia, hepatitis, meningitis, shingles, and chicken pox in immunocompromised patients as well as in some who have normally functioning immune systems.

Committee members emphasized that most of the problems occurred in those with immunocompromising conditions, which can increase susceptibility to live viruses that are in MMR and varicella vaccines.

In general, injection of vaccine can trigger fainting and shoulder inflammation, the group reported.

In the "favors acceptance" category, the committee suggested that certain vaccines can lead to four other adverse events, which include short-term shoulder pain in some women and children who receive the MMR vaccine, anaphylaxis with the HPV vaccine, and mild temporary oculo-respiratory symptoms in flu vaccines used abroad.

They concluded that other vaccines are not linked to four specific conditions, all of which have fueled parent concerns about immunizations. The committee wrote that the MMR and DTaP vaccines don't cause type 1 diabetes and that the MMR vaccine does not cause autism. Their review also found that the flu vaccine doesn't cause Bell's palsy or exacerbate asthma.

Clayton said that more than 100 vaccine adverse event pairs fell in the inadequate data category. One was the seasonal flu vaccine and Guillain-Barre syndrome (GBS), an acute, inflammatory peripheral neuropathy. She told reporters that epidemiological studies have not found a link, but there were problems with some of them.

She said it's difficult to tease out a GBS link to the flu vaccine, because its prevalence coincides with flu season and can be caused by a lot of other confounders. Clayton also said flu vaccines change from year to year, adding another layer of difficulty to the analysis.

In response to reporters' questions, Clayton and other committee members said they hoped the report would be a useful resource for physicians and parents, but they acknowledged that their focus on characterizing the connection between the vaccine and individual adverse events may still leave the public with questions about how frequently such events occur and how to balance the benefits of vaccines against rare side effects.

See also:

Aug 25 IOM adverse events in vaccines report

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