Although child vaccination rates have stayed high, there has been growing concern among parents that vaccines might cause autism. Autism rates in developing countries have risen remarkably in the past 20 years, as studies have shown that, of the children born in 2004, about 1 in 68 children would receive an ASD diagnosis.
It is difficult to compare autism rates from the 1990s and rates from the 1940s to1980s. In the earlier years, the rate of autism was estimated to be only about 1 in 10,000 people, and autism was associated primarily with very severely affected individuals. However, beginning in the 1990s, as a result of improved understanding of the spectrum of autism, individuals who would n’t have been thought of as having autism may now be classified with one of a variety of ASDs.
The probable reasons for the high rates of autism today is still unknown. It could be due to increased diagnosis and reporting, or changing definitions of autism or an actual increase in development of ASD is unknown. Regardless, researchers and some worried parents alike have speculated about the role of vaccines in causing autism.
This has been questioned, along with other possible risk factors for ASD, such as genetic predisposition, advanced parental age, and other environmental factors. Vaccines have entertained more scrutiny than any other speculated cause of ASD, but yet, a majority of scientists, physicians, and public health researchers still concludes that there is no correlation between vaccines and autism. However, the public health and medical establishments still continue to address these concerns.
The MMR Hypothesis
A very shocking revelation emerged sometimes back when a senior researcher stepped forward to admit that the US Centers for Disease Control and Prevention (CDC) had covered up evidence that vaccines are linked to autism. He claimed that the cover-up was systematic and deliberate, and might have caused many children and their families, unnecessary pains.
The vaccine in focus then was MMR (Measles, Mumps, and Rubella) combination vaccine. There was a theory in the past that the age when you receive this vaccine influences the risk of autism. However, this theory was later rejected, and the MMR was declared safe by the CDC. Subsequently, a study that played a significant role in supporting the use of the MMR vaccine at an early age was published in 2004.
It was submitted by DeStefano and his colleagues, and one of the co-authors, Dr. William Thompson, and published in the peer-reviewed journal of Pediatrics. It was one of the co-authors, Dr. William Thompson who blew the whistle and decided to disclose the true data behind the study. It was also alleged that the journal where the original study was published receives financial support from vaccine makers for both advertising and direct donations.
Similarly, in 1995, a group of British researchers published a cohort study in the Lancet, claiming that individuals who had been vaccinated with the measles-mumps-rubella vaccine (MMR) were more likely to have bowel disease than individuals who had not received MMR. Andrew Wakefield MD, a gastroenterologist was one of the researchers, and he went on to further study a possible link between the vaccine and bowel disease. He speculated that persistent infection with vaccine virus caused disruption of the intestinal tissue that in turn led to bowel disease and neuropsychiatric disease (autism).
To add more credence to the claim, Fudenberg, in a small pilot study published in a non-mainstream journal, supported this relationship. Likewise Gupta in a review of possible treatments for autism.
In 1998, Wakefield published a case series study in The Lancet, along with 12 co-authors claiming that they found evidence, in many of the 12 cases of their studies. They claimed to have found the presence of measles virus in the digestive systems of children who had exhibited autism symptoms after MMR vaccination. Even though they could not demonstrate a causal relationship between MMR vaccination and autism, Wakefield still suggested in a video that was released to the public that a causal relationship existed between the MMR and autism.
Over the next couple of years, the possibility of a link between MMR and autism has been studied exhaustively, but yet, no reputable, relevant study has confirmed Wakefield’s findings. These many well-designed studies have, however, found no link between MMR and bowel disease or MMR and autism.
In 2004, in a television interview, then-editor Dr. Richard Horton of The Lancet claimed that Wakefield had been paid by attorneys seeking to file lawsuits against vaccine manufacturers and that his research was “fatally flawed.” Following this, most of the co-authors of the study retracted the interpretation in the paper, and in 2010, The Lancet formally retracted the paper itself.
A couple of months after the retraction, Britain’s General Medical Council banned Wakefield from practicing medicine in Britain, stating that he had shown “callous disregard” for children in the course of his research. The council also uncovered information about the extent to which Wakefield’s research was funded by lawyers who planned to sue vaccine manufacturers on behalf of parents of children with autism.
Following this development, in 2011, a British journalist who had previously reported on flaws in Wakefield’s work claimed to have spoken with parents of children from the retracted study and found evidence that Wakefield committed research fraud by falsifying data about the children’s health conditions.
A great damage was done to public health caused by this tiny study, a study that turned out to be almost entirely fraudulent, but whose impact continues to this day. Although the findings of Wakefield’s paper have long been discredited by scientists, the evidence that the data itself was falsified has remained a landmark moment in the history of vaccines.
The Thimerosal Hypothesis
MMR is not the only vaccine or vaccine component that has been targeted for scrutiny by those who suspect vaccination has a relationship to autism. After the MMR controversy died down, critics turned their attention to thimerosal, a mercury-containing preservative used in some vaccines.
It can be recalled that in the late 1990s lawmakers, environmentalists, medical and public health workers alike, all became concerned about environmental exposures to mercury, with emphasis on consumption of fish. This led to the U.S. Food and Drug Administration (FDA) in 1999 requesting that drug companies report on amounts of mercury in their products. The findings were that results for mercury in vaccines, in the form of thimerosal, exceeded FDA guidelines for exposures to the kind of mercury found in fish.
Mercury found in fish appears in the form of methylmercury, which is not readily metabolized by the human body and excreted. At certain levels of high exposure, it is believed to cause harmful neurological effects. The mercury found in thimerosal metabolizes in the body to ethylmercury, a compound that was thought to be much less harmful than methylmercury.
The FDA, being caught in a dilemma, called for vaccine companies to reduce or eliminate the use of thimerosal in vaccines, as additional studies were planned to investigate whether there were harmful effects in children exposed to the amount of mercury in vaccines.
The Institute of Medicine undertook a comprehensive safety review of the issue, and their preliminary report stated that the committee did not find enough evidence to support or reject a causal relationship between mercury in vaccines and neurodevelopmental disorders.
However, their final report, which was published in 2004, concluded that the large body of evidence gathered on the question favored rejecting the hypothesis that mercury in vaccines was associated with neurodevelopmental disorders. Since then, more evidence from many other studies has continued to support rejecting an association between thimerosal and autism.
Most scientific and medical experts are satisfied that there is no correlation between vaccines and autism or other neurodevelopmental disorders. However, critics continue to question the relationship between MMR and thimerosal and autism. They bring up further culprits they believe might have played a role in the development of autism. To this end, researchers have continued to examine these questions, and are yet to find evidence that these factors play a role in autism development.
Most autism researchers believe that the causes of autism are many and include genetic and environmental factors. The role of vaccines in causing autism is yet to be scientifically established.
Related Scientific Articles
Taylor LE, Swerdfeger AL, Eslick GD. Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies. Vaccine. 2014 June;32(29):3623–3629.
Schechter R, Grether JK. Continuing increases in autism reported to California’s developmental services system: Mercury in retrograde. Arch Gen Psychiatry. 2008;65:19-24.
Institute of Medicine. Immunization Safety Review. Vaccines and Autism Board of Health Promotion and Disease Prevention, Institute of Medicine (National Academy Press, Washington, DC, 2004).
Hviid A, Stellfeld M, Wohlfahrt J, Melbye M. Association between thimerosal-containing vaccine and autism[PDF – 145 KB]. JAMA. 2003;290:1763–6.
Madsen KM, Hviid A, Vestergaard M, Schendel D, Wohlfahrt J, et al. A population-based study of measles, mumps, and rubella vaccination and autism. N Engl J Med. 2002;347 (19):1477–1482.
Ball L, Ball R, Pratt RD.An assessment of thimerosal in childhood vaccines. Pediatrics. 2001;107:1147–1154.
Joint statement of the American Academy of Pediatrics (AAP) and the United States Public Health Service (USPHS). Pediatrics. 1999;104:568–9.
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