Sunday, August 28, 2011

Few Adverse Events Linked to Vaccines, IOM Panel Says

From Medscape Medical News Robert Lowes August 25, 2011 — Only a small number of adverse events are caused by or clearly linked to a group of 8 vaccines, and scientific evidence favors rejecting a causal relationship between the vaccine for measles, mumps, and rubella (MMR) and autism, according to a report issued today by an expert committee of the Institute of Medicine (IOM). "The findings should be reassuring to parents that few health problems are clearly connected to immunizations, and these effects occur relatively rarely," said committee chair Ellen Wright Clayton, MD, JD, a professor of pediatrics and law at Vanderbilt University in Nashville, Tennessee, in a press release. "And repeated study has made clear that some health problems are not caused by vaccines." Analyzing more than 1000 research articles, the IOM committee weighed epidemiological, clinical, and biological evidence for adverse events associated with the 8 vaccines. In addition to the MMR vaccine, the vaccines examined are the varicella zoster vaccine, influenza vaccines (other than the 2009 H1N1 influenza vaccine), hepatitis B vaccine, human papillomavirus (HPV) vaccine, tetanus toxoid-containing vaccines other than those containing the whole-cell pertussis component, hepatitis A vaccine, and meningococcal vaccines. All 8 vaccines are covered by the National Vaccine Injury Compensation Program, and the IOM expects that the committee findings will provide the program with scientific guidance as it adjudicates injury claims. The committee reached 158 conclusions about a cause-and-effect relationship between each of the vaccines and a plethora of adverse events. In the vast majority of cases, the group decided that the evidence is inadequate to accept or reject a causal relationship. No one should construe such a determination to mean that a vaccine is either safe or unsafe, according to the committee, which noted that it never intended to make judgments on vaccine safety per se. "Policy determining vaccine use requires a balancing of risks and benefits," the report stated. "That is outside the bounds of this committee's assignment." MMR Vaccine/Autism Review Included Retracted Article by Andrew Wakefield Three other sets of conclusions about causality offer more guidance. The group decided that the evidence "convincingly" supports a link between anaphylaxis and MMR, varicella, influenza, hepatitis B, meningococcal, and tetanus toxoid vaccines; febrile seizures and MMR vaccine (such seizures almost always have no long-term consequences); syncope and the injection of any vaccine; deltoid bursitis and the injection of any vaccine; disseminated Oka-strain varicella zoster virus, along with Oka-strain varicella zoster virus viral reactivation (both with and without other organ involvement) and varicella vaccine; and measles inclusion body encephalitis and MMR vaccine in individuals with severe immune system deficiencies. According to another set of committee conclusions with a lower certainty level, scientific evidence favors accepting a causal relationship between anaphylaxis and HPV vaccine, transient arthralgia in adult women and MMR vaccine, transient arthralgia in children and MMR vaccine, and a mild and temporary oculorespiratory syndrome and certain trivalent influenza vaccines in Canada. Conversely, the committee stated that the evidence favors rejecting a causal relationship between type 1 diabetes and MMR vaccine; type 1 diabetes and diphtheria, tetanus, and pertussis vaccine; Bell's palsy and inactivated influenza vaccine; asthma exacerbation or reactive airway disease episodes and inactivated influenza vaccine; and autism and MMR vaccine. In its deliberation on MMR vaccine and autism, the committee stated that it reviewed 22 studies for epidemiologic evidence but relied only on 5 that, unlike the others, were "reasonably valid" overall. Each of the 5 studies asserted that there is no causal relationship between the vaccine and autism. The committee also reviewed 4 articles and weighed evidence for the biological mechanisms by which MMR vaccine could possibly trigger autism. Its report noted that one of those articles, authored by the controversial Andrew Wakefield, was retracted last year by its publisher, The Lancet. Earlier this year, a series of articles and editorials in the British Medical Journal called Wakefield's article an "elaborate fraud." "The committee assesses the mechanistic evidence regarding an association between MMR vaccine and autism as lacking," the report stated.

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