Do Vaccines Cause Autism? | History of Vaccines
scientific studies that clearly show no link between the. MMR vaccine and autism (refer to Vaccine Safety: Examine the Evidence using the link. Additional population-based studies considered the relationship between MMR vaccine and the “new variant” form of autism proposed by Wakefield et al. The research is clear: Vaccines don't cause autism. More than a dozen studies have tried to find a link. Each one has come up empty.
Boy with measles Centers for Disease Control and Prevention Autism rates in developing countries have risen remarkably in the past 20 years. For children born inaccording to the U. For children born inabout 1 in 68 children would receive an ASD diagnosis. The role of vaccines has been questioned, along with other possible risk factors for ASD, such as genetic predisposition, advanced parental age, and other environmental factors.
Vaccines have perhaps received more scrutiny that any other speculated cause of ASD, and the great majority of scientists, physicians, and public health researchers have come to the conclusion that there is no association between vaccines and autism.
The MMR Hypothesis The story of how vaccines came to be questioned as a cause of autism dates back to the s. Part of this hypothesis — that vaccination was associated with autism — had been suggested previously a few researchers.
For example, Fudenberg, in a small pilot study published in a non-mainstream journal, posited this relationship, as did Gupta in a review of possible treatments for autism. InWakefield, along with 12 co-authors, published a case series study in the Lancet claiming that they found evidence, in many of the 12 cases they studied, of measles virus in the digestive systems of children who had exhibited autism symptoms after MMR vaccination.
Wakefield himself had filed for a patent for a single-antigen measles vaccine in and so would seem to have a potential financial interest in promoting this view. Press outlets covered the news widely and frightened parents began to delay or completely refuse vaccination for their children, both in Britain and the United States.
MMR vaccination rates in Britain plummeted. After examining the records for all twelve children, Deer noted that the statements made in the paper did not match numbers from the records in any category: The Lancet paper claimed that six of the children had all three of these conditions; according to the records, not a single child actually did.
In an accompanying editorial, BMJ editor in chief Fiona Godlee and co-authors Jane Smith and Harvey Marcovitch examine the damage to public health caused by a tiny study based on parental recall with no control group — a study that turned out to be almost entirely fraudulent, but whose impact continues to this day.
Evidence is strong that the original study should not have been published not merely because it was poorly conducted, but also because it was a product of research fraud. The Thimerosal Hypothesis MMR is not the only vaccine or vaccine component that has been targeted for scrutiny by those who suspect vaccination might be related to autism.
After the MMR controversy died down, critics turned their questions to thimerosal, a mercury-containing preservative used in some vaccines. Thimerosal had never been used in MMR, as antimicrobial agents are not used in live vaccines.
With heightened attention to known and potential harmful effects of such exposures, the U. Food and Drug Administration FDA in requested that drug companies report on amounts of mercury in their products. The results for mercury in vaccines, in the form of thimerosal, exceeded FDA guidelines for exposures to the kind of mercury found in fish.
Mercury in fish appears in the form of methylmercury, which is not readily metabolized and excreted in the human body. It is known to cause, at certain levels of high exposure, harmful neurological effects.
The mercury in thimerosal metabolizes in the body to ethylmercury, a compound that, while not widely studied at the time, was thought to be much less harmful than methylmercury. Should they apply the methylmercury guidelines to ethylmercury?
Vaccines Do Not Cause Autism
A meta-analysis is a mathematical synthesis of the results of the studies included. This is an appropriate way of pooling and studying the body of available evidence on a specific topic. What did the research involve? The researchers searched databases of published literature to identify case-control and cohort studies that have assessed the relationship between vaccine administration and the subsequent development of autism or autism spectrum disorder.
Studies were included that looked at measles, mumps and rubella MMR vaccinationcumulative mercury, or cumulative thimerosal dosage from vaccinations.
Thimerosal is a mercury-containing chemical that acts as a preservative. The researchers then performed a meta-analysis to combine the results of the studies included in the review. What were the basic results? The researchers included five cohort studies involving 1, children, and five case-control studies involving 9, children. None of the five cohort studies found an association between vaccination and autism or other autism spectrum disorder.
When the results of the five cohort studies were combined, there was no increased risk of developing autism or autism spectrum disorder after MMR, mercury or thimerosal exposure odds ratio [OR] 0.
Vaccines Do Not Cause Autism Concerns | Vaccine Safety | CDC
The researchers performed subgroup analyses looking at autism and autism spectrum disorder separately. There was no increased risk of developing autism OR 0.
They then performed subgroup analyses looking at the different exposures separately. There was no increased risk of developing autism or autism spectrum disorder after MMR vaccination OR 0. The researchers also looked at whether there was any evidence of publication biasa bias that can occur if the publication of research results depends on the nature and direction of the results.
Typically, positive results tend to get published while negative results get shelved. If this occurs, it can distort the results of systematic reviews and meta-analyses. The researchers analysed the results of the cohort studies using statistical tools and found no evidence of publication bias.