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The MMR Immunization and Autism: Does correlation mean causation?
A review by Leigh Forbush
October 24, 2008
Since the discovery of the germ theory and the first use of inoculations in the 19th century, childhood immunizations have become an assumed practice for the majority of Americans. A slew of vaccinations including Hepatitis B, Diphtheria and Influenza are strongly recommended for children by public health experts, physicians and school boards dating from infancy. While much of the aging American population, including the baby boom generation, has seen first-hand the effect vaccinations have had on controlling epidemics, the power of immunizations have left many young parents and children today without visible proof of the importance of vaccinations. Instead, many American parents now oppose immunizations, particularly childhood immunizations, as information about possible dangers to children have circled via modern channels of communication. Particularly, the childhood Measles, Mumps and Rubella (MMR) vaccine has been connected to the appearance of Autism in children, and has led to the formation of anti-vaccination groups and increased rates of vaccination exemption within schools.
Why are vaccinations such as the MMR seemingly necessary? What are the popular beliefs driving the rejection of vaccines? Finally, is there really a link between vaccinations and Autism? The following sections will review both common information surrounding vaccinations and scientific research specifically studying the correlation of the MMR vaccine and Autism.
What is a Vaccination? Why are Vaccinations Important?
Firstly, vaccinations are preparations used as preventative measures to develop immunity against a specific disease through the injection of an innocuous form of the disease agent, or through injection of a weakened bacteria or virus to stimulate antibody production (http://dictionary.reference.com/browse/vaccine). Vaccinations, according to the Centers for Disease Control and Prevention, are crucial in helping protect the population and individuals from disease and the subsequent spread of disease. Vaccinations are responsible for eliminating many of the infectious diseases no longer common today, and children are especially at risk for infectious diseases because their immune systems are not as strong as adults, leading to higher mortality rates if infected (http://www.cdc.gov/vaccines/vac-gen/importance.htm).
What is the MMR Vaccination? What is Autism?
The Measles, Mumps and Rubella Immunization, better known as the MMR immunization, is a 3-in-1 vaccine that protects against measles, mumps and rubella, all of which are potentially dangerous childhood illnesses. This immunization first released in 1988 is a shot composed of freeze-dried live attenuated measles, mumps and rubella viruses. The immunization causes a 90% protection rate against measles and mumps, and 95% protection rate against rubella (http://www.patient.co.uk/showdoc/40025003/). Measles, mumps and rubella, although uncommon today, cause symptoms that range from fever, to deafness, to death. The MMR vaccination is a recommended childhood immunization that is typically required for school entry. The immunization consists of two shots, one of which is to be given at 14-15 months old, and the other between 4-6 years old (http://www.nlm.nih.gov/medlineplus/ency/article/002026.htm).
Autism, on the other hand, is a developmental disorder first established in 1938 and is diagnosed in toddlers usually 12-24 months old. Autism is characterized by impaired social interaction, problems with verbal and nonverbal communication, and/or severely limited activities and interests. Autism affects 0.6% of the population and its symptoms can range from severe to mild. There is no current cure for Autism and therapy and behavioral interventions are used to improve many autistic symptoms (http://www.ninds.nih.gov/disorders/autism/detail_autism.htm).
Why is There Believed to be an Autism-MMR Link?
Beginning in 1991 with the classification of Autism as a childhood disorder meriting special education services by the US Department of Education, heightened public awareness and media coverage concerning the causes and treatments of Autism has grown steadily. As cited by BBC News online, the first claims about a link between Autism and the MMR vaccination was made in 1998 by Dr. Andrew Wakefield, a doctor in experimental gastroenterology at London’s Royal Free Hospital. He published a description of 12 cases in which toddler patients receiving the MMR vaccine developed gastrointestinal disorders that led to an increased risk in developing developmental disorders, such as Autism. In 2000, Wakefield came out with a more comprehensive scientific study of 25 autistic children, 24 of which seemingly had traces of the measles virus in their gut (MMR, 2008). Although Wakefield did not mention that the measles virus in the gut was caused by the receipt of the MMR vaccine, nor did he prove that the development of autism is due to measles, he did mention the correlation between Autistic children who received the MMR vaccination and developed gastrointestinal disorders. Many citizens took Wakefield’s study very seriously and believed that the correlation of symptoms meant the causation of symptoms (http://www.nichd.nih.gov/publications/pubs/autism/mmr/sub2.cfm). This study had a large international impact, frightening many parents to abstain from immunizing their children with the MMR vaccine and forcing many scientists scrambling to study this phenomenon. Wakefield’s study first introduced the connection between Autism and the MMR vaccine, which has since fueled the controversy of childhood immunizations.
Dr. Wakefield, with wife
What do anti-MMR vaccination groups think?
Many people who reject vaccinations for their children focus on the popular belief that the MMR vaccine causes Autism. Those who are against the MMR immunization voice their opinions through online blogs, forums and groups and are mainly parents of autistic children searching for an environmental cause of autism. These parents often cite the Wakefield study, as well as governmental reports to prove the link, or at least a possible connection, to Autism and the MMR immunization.
Reasoning against the MMR vaccine
Specifically, many of parents believe that Autism is linked to the MMR vaccination through the mercury-based thiomersal, a preservative found in the MMR vaccine. One report by the FDA in 1997 is often cited by anti-MMR groups as governmental evidence that demonstrates the link between vaccine dangers and developmental disorders. This study, sponsored by the FDA Modernization Act, reviewed all mercury containing food and drugs as a general assessment. The FDA’s findings concluded that the amount of lead found in infant vaccines were higher than the EPA recommended amount for exposure in infants, although it did not exceed the FDA or WHO standards. The concerns about the neurological effects of mercury on infant health, although only researched through the effects of methyl-mercury, worried much of the population who were increasingly aware of the dangers of lead (http://www.fda.gov/cber/vaccine/thimerosal.htm). Therefore, the FDA suggested in the 1997 report that they would slowly try to remove lead from all factions of life, including vaccines, to increase the support from the public. In a follow-up report on the public’s general view of immunizations in 2001, the National Academies of Science’s Institute of Medicine concluded “that the evidence is inadequate to accept or reject a causal relationship between thimerosal exposures from childhood vaccines and the neurodevelopmental disorders of autism” (Stratton et al., 2007, page 4). Many Americans took the voluntary removal of thiomersal from vaccines and the National Academies of Science’s ambiguous statement to signify a plausible link between the two. As one blogger testifies in his “Age of Autism” journal, “I’m not going to repeat myself here except to say, there’s every reason to worry about the interaction among live viruses when you stick ‘em in the same shot and inject ‘em into 12-month-old kids. Especially kids whose immune systems are already shot thanks to vaccine mercury and other toxins” (http://www.ageofautism.com/2008/02/mmr-and-the-sim.html).
Finally, many parents believe the MMR vaccine causes Autism because of the timing of the proximity in injection/development of the MMR immunization and onset symptoms of Autism. Many parents observe that immediately after, or months after the receipt of the first MMR injection at age 14-15 months, their children undergoes behavioral regression. While their child seemed to be developing normally in the first year of life, after receipt of the MMR vaccine their child has developed Autism (http://www.dukehealth.org/HealthLibrary/AdviceFromDoctors/YourChildsHealth/mmr_vaccine_and_autism). Because no definite causes of Autism (either genetic or environmental) have yet been discovered, parents have started making conclusions based on their personal experience and observations. However, these online blogs and forums cannot be trusted as reliable sources of information because they rely on illness narrative rather than scientific knowledge that supports their claims.
Anti-MMR Use of Publicity To Spread Message
People against the MMR vaccination also use publicity from celebrities to highlight their cause and spread their message, notably actors Jenny McCarthy and Jim Carrey, who have an autistic son. Only this past year, McCarthy and Carrey rallied against childhood vaccines, claiming that too many immunizations are required too soon in infancy. Their voices were heard on a national scale through a “Green Our Vaccines Rally”, claiming that there is a link between vaccine toxicity and autism (http://www.talkaboutcuringautism.org/jenny/dc-rally/green-our-vaccines-rally.htm). As well, multiple court cases involving parents suing doctors and government health departments have been given considerable media attention, fueling the energy and publicity of anti-vaccination groups. The recent 2008 Hannah Poling Autism case made national news when the Polings won their lawsuit suing the Department of Health and Human Services for making their daughter autistic through vaccinations (Poling, 2008). Anti-MMR activists cite the lawsuit as a success that proves the danger of vaccinations.
Jenny McCarthy and Jim Carrey
What does the Public Health/Medical Profession Think?
Governmental Health Institutions
On the other hand, many renowned and respected governmental and independent medical websites have denied the link between the MMR vaccine and Autism. The Center for Disease Control and National Insitutes of Public Health both have pages upon pages of information regarding the importance of childhood vaccinations and they even specifically address questions concerning the safety of vaccines and the rumored connection with Autism. These governmental agencies cite many facts against any possible connection, claiming that Wakefield’s study was limited in scope and findings, and that many of the original authors of the Wakefield study have since renounced the connection between the MMR immunization and Autism. The CDC mentions other important studies that have disproved any link between the two and finally encourages the websurfer to other sites such as the CDC’s Autism Information Center where more information can be given (http://www.cdc.gov/vaccinesafety/concerns/mmr_autism_factsheet.htm). As quoted by the NIH, “to date there is no definite, scientific proof that any vaccine or combination of vaccines can cause autism. It’s important to know that vaccines actually help the immune system to defend the body” (http://www.nichd.nih.gov/publications/pubs/autism/mmr/sub2.cfm).
Medical Resources Online
As well, many universities, hospitals and online medical news sources have more objective webpages that discuss the link between MMR and Autism. These webpages, such as Medpage Today and Duke University Health System, clarify popular beliefs by stating both sides of the controversy but that similarly conclude that there is no connection between the two as cited in research studies (http://www.dukehealth.org/HealthLibrary/AdviceFromDoctors/YourChildsHealth/mmr_vaccine_and_autism). These medical webpages usually continue to state that immunizations are necessary for the decrease of infectious diseases. Whereas the anti-vaccination groups focus on personal observation, the public health community cites scientific studies from across the globe, and thus can be considered more objective as a source of information.
Scientific Literature– Is there really a link between MMR and Autism?
The increase in Autism despite MMR withdrawal
The publication of Dr. Wakefield’s study in 1998, along with profuse media coverage of immunizations and Autism, has lead to an enormous amount of research studies examining whether a link between the MMR vaccination and Autism actually exists. One populational study, centered in Yokohama, Japan in 2005, is heralded as one of the most decisive studies proving no connection between the MMR vaccine and Autism. Particularly, this study examined the rate of development of Autism Spectrum Disorders (ASD) during an MMR vaccination program and after the MMR vaccination program had been discontinued. The researchers first looked at the yearly cumulative incidence of Autism in children up to seven years old who were born from 1988-1996 in the Kohoku Ward of Yokohama and had received the MMR vaccine. Then, researchers studied the incidence of children with Autism in that same birth cohort when the MMR vaccination rate declined from 1988-1992, with finally no vaccination being administered in 1993 or after. Instead, single shots of measles, mumps and rubella were injected separately at different points in childhood starting in 1993. The 31,426 children in the birth cohort of this study were monitored for signs of Autism through the Yokohama Rehabilitation Center, with specific criteria identified by the Young Autism and other developmental disorders Checkup Tool (YACHT) and IQ tests. Children were first screened at age 18 months and regularly thereafter for Autism symptoms. Researchers finally concluded that the cumulative incidence of Autism disorders increased during the birth cohorts of 1988-1996 from 47.6 per 10,000 children in 1988 to 117.2 per 10,000 children in the 1996 cohort. Interestingly, there was a sharp rise in Autism in 1993, regardless of the MMR vaccine being discontinued at this time.
Looking at the rise in autism despite the cancellation of the MMR vaccination, the researchers determined that it is highly unlikely the MMR immunization causes Autism. As the title of the study states, there is “No effect of MMR Withdrawal on the Incidence of Autism”. The rise in Autism cannot be linked to an increased use of the MMR vaccine (Honda, 2005).
A replica of Dr. Wakefield’s study – No connection of onset symptoms
Another scientific case-control study preformed in 2008 specifically tried to replicate Dr. Wakefield’s study in order to determine whether children with gastrointestinal disturbance autism actually have measles virus RNA in the bowel tissues and if this relates to the receipt of the MMR vaccine. The measles virus has been thought to create gastrointestinal inflammation which creates chemicals leading to development neuropathology, exemplified in Autism. The sample used in the case-control study was 25 children with autism and gastrointestinal disturbances that were compared with 13 children with just gastrointestinal disturbances. The median age from receipt of first MMR vaccination was similar for the cases and controls, and none of the children had received any other measles-containing vaccinations. Bowel tissues from both groups were sampled and evaluated in laboratories blinded to diagnosis for the presence of the measles virus. The researchers also examined the temporal relationship between the MMR vaccination, the first gastrointestinal episode and the onset of Autism; the MMR vaccination must precede the gastrointestinal dysfunction which must precede the onset of Autism. However, only 20% of subjects received the MMR vaccine before the onset of gastrointestinal difficulties that were also before the onset of Autism. The researchers concluded that the time of exposure to the MMR vaccine relative to the onset of gastrointestinal dysfunction and autism were inconsistent with MMR as a trigger to gastrointestinal disturbances or Autism.
As well, the researchers concluded from the bowel tissue results that there were not significant differences between the case and control groups of the presence of the measles virus RNA across the three laboratories. Overall the study proved that the onset of gastrointestinal and Autism symptoms are unrelated to the receipt of the MMR immunization (Hornig, 2008).
Autism-MMR Vaccine Literature Review
Finally, because the link between Autism and the MMR immunization became such a popular topic to research in response to Dr. Wakefield’s initial study in 1998, literature reviews of the various scientific studies have become important to use to condense all the findings. One of these reviews of current epidemiological evidence, “Association of Autistic Spectrum Disorder and the Measles, Mumps and Rubella Vaccine” chose 12 of 379 potential epidemiological articles examining an association between Autism and the MMR vaccination. These articles spanned 5 countries and from populations dating back as early as 1954; these studies included time-series analyses, cross-sectional studies, and retrospective cohort studies. Specifically, one study showed no difference in the rates of Autism and MMR vaccine for those who were vaccinated and those who were not. Six of the studies showed that there was an increase in Autism with an increase in received MMR immunizations; however none of these studies showed any type of association between Autism and the MMR vaccine. Eight of the 12 studies examined if there was temporal association between developing Autism and receiving the MMR vaccination. The researchers were able to conclude that current literature does not propose an association with the MMR immunization and Autism. However, there is also little evidence to eliminate a link between a rare form of Autism and the MMR vaccine. Considering the larger risks involved with not immunizing children and the fact that no link is scientifically proven between the MMR vaccine and Autism, the authors determined that current policies should still encourage the use of the MMR vaccines in children (Wilson et al., 2003).
Reviewing both general information found on the internet as well as scientific literature, it is evident that there is no proven link between Autism and the receipt of the MMR immunization. The multiple scientific studies researched in different countries have shown that a global increase in Autism has occurred even with the decrease and elimination of thimerosal and the MMR vaccination. Furthermore, the primary study by Wakefield which incited the initial linkage (and is still the only real study proving possible causation between the MMR vaccine and Autism), has since been heavily criticized and even rejected in repeat studies. Instead, many of the anti-MMR claims popular on the internet are made by parents and lay people who merely have observed a correlation between the timing of the receipt of the MMR vaccine and onset symptoms of Autism. Although it is well known that the receipt of the MMR immunization and the first visible symptoms of Autism occur at similar times, those against the MMR vaccine relate correlation with causation, which are very different diagnoses.
Additionally, many parents are still wary of childhood immunizations despite scientific studies due to the large media attention directed at the MMR vaccine and Autism in the late 1990s and early 2000s. The extensive influence and coverage of the safety of vaccines concerning Wakefield’s study permeated the minds of many Americans who were unaware of the true facts of the MMR-Autism connection (or lack thereof). In reality, a study in 2007 demonstrated that 48% of the media coverage on autism has focused on the environmental causes, although only 13% of published research is about possible environmental triggers (http://www.sciencedaily.com/releases/2007/01/070130184737.htm). Many more citizens respond to ideas cited by celebrities rather than scientific literature, which in effect, has significantly damaged the reputation and rate of usage of an important childhood immunization. By refusing childhood immunizations, parents are essentially helping to “undo the progress we have made over the years” (http://www.cdc.gov/vaccines/vac-gen/why.htm) – something that we simply cannot afford as a society. Although as for every vaccination there are possible side effects, it is much more important from a public health standpoint to receive immunizations to combat the spread and resurgence of many diseases rarely seen in America today. So, if considering whether or not to let a child receive the MMR vaccination, know that there is truly no proven link between Autism and the vaccination. In fact, your child will be put at more risk through the exemption of vaccinations!
Honda, Hideo et al. (2005). No effect of MMR withdrawal on the incidence of autism: a total population study. Journal of Child Psychology and Psychiatry, 46:6, 572–579.
Hornig M, Briese T, Buie T, Bauman ML, Lauwers G, et al. (2008). Lack of Association between Measles Virus Vaccine and Autism with Enteropathy: A Case-Control Study. PLoS ONE 3(9): e3140. doi:10.1371/journal.pone.0003140.
MMR Research Timeline (2008, February 4). BBC News, pp. 1. Retrieved October 6, 2008 from http://news.bbc.co.uk/go/pr/fr/-/2/hi/health/1808956.stm
Poling, J.S., Offit, P.A. (2008). Vaccines and Autism Revisited. NEJM 359, 655-656.
Stratton, K., & Gable, A., & McCormick, M.C. (Eds.) (2001). Immunization Safety Review: Thimerosal-Containing Vaccines and Neurodevelopmental Disorders. Washington D.C.: National Academy Press.
Wilson, Kumanan et al. (2003). Association of Autistic Spectrum Disorder and the Measles, Mumps and Rubella Vaccine. Archives of Pediatric and Adolescent Medicine 157, 628-634.
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