Vaccine Link To Autism Refuted In Defining Report
Institute Of Medicine Says Findings Conclusive
A US government panel has concluded decisively that childhood vaccinations do not cause autism, according to a report issued recently.
Since concerns about a suspected link were first raised in the late 1990s, many scientific studies have refuted this association. The latest Institute of Medicine (IOM) report referred specifically to the measles-mumps-rubella (MMR) vaccine as well as to vaccines that at one point contained the mercury-based preservative thimerosal.
Considerable debate has been conducted for many years as to whether these might trigger the onset of autism in small children.
Approximately 15 out of every 10,000 children born are diagnosed with autism. Autism is more prevalent in boys than girls, with four times as many boys affected than girls.
Although it is not clear whether this debate will ever be put completely to rest, the report is very "close to the final word," says Dr. Tom Saari, a professor of pediatrics at the University of Wisconsin Medical School in Madison and a member of the American Academy of Pediatrics (AAP) committee on infectious diseases.
"It's clearly not going to settle it for some people, but it clearly suggests that there are other avenues that are much more profitable to pursue in terms of trying to understand what autism is and how to both prevent and treat it," says Dr. Marie C. McCormick, head of the IOM Immunization Safety Review Committee and a professor of maternal and child health at the Harvard School of Public Health.
"The overwhelming evidence from several well-designed studies indicates that childhood vaccines are not associated with autism," Dr. McCormick says.
Concerns Raised a Decade Ago
The controversy regarding autism and vaccines began in 1998 with the publication of a case series describing 12 children with pervasive developmental disorder, eight of whom exhibited behavioral problems their parents and physicians said coincided with receiving the MMR vaccine.
This question of timing is one argument supporters of the vaccine-autism link have used to further their point of view.
"The timing issue certainly affects the perception of an association between MMR and autism, because MMR is given in the second year of life, which is when symptoms of autism tend to be more evident," Dr. McCormick says.
Another issue is the fact that, until 1999, the preservative thimerosal was used in more than 30 vaccines licensed and marketed in the US.
That year, the US Food and Drug Administration determined that small children receiving the standard vaccination schedule might be exposed to cumulative doses of ethylmercury that exceeded some safety guidelines. Measures were quickly taken to remove thimerosal from these vaccines.
The IOM had already published two reports on possible links between autism, the MMR vaccine, and thimerosal. Those reports concluded there was no evidence to support a link between MMR and autism, but there was not enough evidence to disprove a thimerosal-autism connection.
In any event, today vaccines given to infants either have no thimerosal or negligible amounts.
Thimerosal is still included in some influenza vaccines but, Dr. Saari says, "The potential exposure a child would get from a flu vaccine is extremely small." And there are thimerosal-free versions available this year, albeit not enough to inoculate everybody.
For the current study, the committee looked at existing research on the subject, namely five studies that explored the thimerosal-autism connection and 14 that looked at MMR and autism. The five thimerosal studies found no association between that compound and autism, while the 14 MMR studies also found no credible connection.
"We have 12 well-designed studies that say it isn't so," Dr. Saari says. "In that particular arena, I think most of us feel very comfortable with the weight of the evidence."
However, the committee determined that five studies found a link between thimerosal and autism, and another two found a connection between MMR and the disease.
The panel concluded the evidence presented was not compelling. "They were not high enough quality to sway the conclusions of the other reports," Dr. McCormick states.
Finally, the committee also concluded that there was insufficient evidence that activation of the immune system by the vaccine somehow triggered autism.
Research Continues on Some Fronts
Some studies will continue to determine if a link exists between autism and vaccines.
Dr. Timothy Buie, an instructor of medicine at Harvard Medical School, is in the middle of a study to see if the measles virus is present in the colon of children with autism.
"We are trying to find out if the presence of the virus is any more relevant in autistic kids," he explains. "We're not sure what we're going to find."
The original 1998 case studies saw GI symptoms in the children that seemed to point to a link between autism and the MMR vaccine.
"I'm not certain there is enough information out there to draw that conclusion [of the IOM]," Dr. Buie says. "There are still not a lot of centers actively looking at the question.
"I think they do deserve a little bit more time and a few more centers to put their two cents in to see if they can find for or find against," Dr. Buie says. "Anything that would lead us to more concern or less concern is of value."
In addition, the Autism Society of America (ASA) states in a press announcement that it is "calling on the government to launch biological and clinical studies that look at the subgroup of individuals with autism who may be genetically susceptible to the effects of vaccines and/or thimerosal before putting this issue to rest."
The ASA states that the IOM should not rely just on broad, epidemiological studies which look at large numbers of people and do not determine cause and effect, but should use the smaller, clinical studies to obtain more specific information.
Always consult your child's physician for more information.
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July 2004
Vaccine Link To Autism Refuted In Defining Report
Concerns Raised a Decade Ago
Research Continues on Some Fronts
Autistic Disorder Defined
Online Resources
Autistic Disorder Defined
Autistic disorder (also called autism) is a neurological and developmental disorder that usually appears during the first three years of life.
A child with autism appears to live in his/her own world, showing little interest in others, and a lack of social awareness. The focus of an autistic child is a consistent routine and includes an interest in repeating odd and peculiar behaviors.
Autistic children often have problems in communication, avoid eye contact, and show limited attachment to others.
Autism can prevent a child from forming relationships with others (in part, due to an inability to interpret facial expressions or emotions).
A child with autism may resist cuddling, play alone, be resistant to change, and/or have delayed speech development.
Persons with autism tend to exhibit repeated body movements (such as flapping hands or rocking) and have unusual attachments to objects. However, many persons with autism excel consistently on certain mental tasks (such as counting, measuring, art, music, and memory).
The cause of autism is not known. Research suggests that autism is a genetic condition. It is believed that several genes are involved in the development of autism.
Research studies in autism have found a variety of abnormalities in the brain structure and chemicals in the brain, but there have been no consistent findings.
One theory is the possibility that autistic disorder is a behavioral syndrome that includes several distinct conditions. However, parenting behaviors are not the cause or a contributing factor to the cause or causes of autism.
For the first time, standard guidelines have been developed to help identify autism in children before the age of 24 months.
In the past, diagnosis of autism was often not made until late preschool-age or later. The new guidelines can help identify children with autism early, which means earlier, more effective treatment for the disorder.
The standardized guidelines were developed with assistance from 11 different organizations and were published in Neurology, a journal of the American Academy of Neurology.
According to the guidelines, all children before the age of 24 months should routinely be screened for autism and other developmental delays at their well-child check-ups. Children that show developmental delays and other behavior disorders should be further tested for autism.
According to the guidelines, less than 30 percent of children undergo age-appropriate screening at their well-child check-ups.
By screening children early for autism, those diagnosed with the disorder can be treated immediately and aggressively.
Always consult your child's physician for more information.
Online Resources
(The Medical University of South Carolina is not responsible for the content of Internet sites.)
American Academy of Neurology
American Academy of Pediatrics
Centers for Disease Control and Prevention (CDC)
National Institute of Child Health & Human Development
National Institute of Mental Health
National Institutes of Health (NIH)
US Food and Drug Administration
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