Do vaccines cause autism?

Sidharth Sanjeev takes a detailed look at the historical scientific controversy surrounding vaccines and autism

Sidharth Sanjeev
26th January 2021
Image credit: Markus Spiske on Unsplash
The end of the last century witnessed the deterioration of people’s trust in vaccines due to a claim in the scientific literature that autism was associated with vaccinations. Over the years, various hypotheses have been formed regarding this claim; however, the cogency of these hypotheses have always been in question. Using multiple studies to discuss and evaluate their validity, each hypothesis will be investigated in turn: first the MMR-vaccine hypothesis, then the Thimerosal hypothesis and finally, present day research on the vaccine-autism link.

MMR-vaccine hypothesis

The controversy initially arose in 1998 when Andrew Wakefield released a study which linked MMR (Measles, Mumps and Rubella) vaccines with autism. His study included autistic children with abdominal pain who underwent neurological and gastroenterological assessments. After procuring the results, he established that the MMR vaccine triggered intestinal inflammation, causing the translocation of non-permeable peptides into the bloodstream and then to the brain: thus hindering its development.

Image credit: Josh Riemer on Unsplash

The study had its own flaws; to begin with, the study sample was quite small (12 children) and did not have a control group. This suggests that there is a very high possibility that the behavioural and intestinal pathologies detected might have occurred coincidentally. Also, the assessments were not double-blind, indicating that the researcher may have shown selection bias while choosing the participants (Plotkin, 2009).

Furthermore, Wakefield makes an erroneous comparison in which he states that, since Rubella virus is associated with Autism, the MMR vaccine is also responsible for autism. This incorrect assumption is a faulty analogy as there is no explanation provided regarding the connection between the virus and the vaccine.

Regardless of its limitations, Wakefield's study paved the way for rightfully questioning the possibilities of the harmful impact of vaccines which were being ignored before

The study also has the red herring fallacy as it sidetracks from its main issue: MMR vaccines cause autism, into a secondary issue, which focuses on MMR vaccines causing intestinal inflammations. Later, Wakefield uses this secondary issue as an explanation behind his main purpose, without having any biological proof for his argument.

Consequently, newer studies are disapproving of Wakefield's arguments, including Hornig (2008), who found that MMR vaccines do not cause any intestinal inflammations. Also, the peptides, which according to Wakefield, travel from the intestine to the brain have not been identified (Plotkin, 2009).

Image credit: CDC on Unsplash

All these factors reveal that the researcher has jumped to conclusions based on hasty generalisations, not empirical research. Hence, the results cannot be applied to the total population. However, regardless of the limitations of the study, one important consequence of the study was that it paved the way for rightfully questioning the possibilities of the harmful impact of vaccines which were being ignored before.

Evidently, the whole blame on MMR vaccines was proved incorrect by a long-term study by Hviid et al (2019). The study’s results can be considered legitimate because the sample represented the target population as it was homogeneous, in terms of ethnicity and socioeconomic status, and also had a large sample size (657461 participants).

Thimerosal hypothesis

After the initial blame towards MMR vaccines was proved false, the accusation shifted towards the role of Thimerosal (type of ethylmercury used in vaccines) in aggravating autism (Bernard et al, 2001). This study compared the similarity of the symptoms of autism and mercury poisoning, concluding that chances of Thimerosal causing autism is likely. It covered a wide variety of symptoms, however there wasn’t enough empirical backing in the study for many symptoms. For example, the study said that lack of eye contact is a symptom of both ailments, but in the case of mercury poisoning, the study mentioned that it was witnessed only in one 12-year-old girl.

Image credit: Caleb Woods on Unsplash

Drawing conclusions based on one patient is not scientifically correct. Bernard also stated that “elevated mercury levels were observed in biological samples of autistic patients,” yet did not provide any references for this statement (Nelson KB and Bauman ML, 2003). Such baseless examples depict that the study heavily depends on hasty generalisations and cannot be relied upon.

Rimland & McGinnis (2002), also focused on the role of Thimerosal in aggravating autism. The study focused on how similar Thimerosal and Methylmercury (a highly dangerous compound) are chemically. However, recent studies have shown that Thimerosal is broken down and excreted much faster than Methylmercury in the human body. Thus, the probability of Thimerosal accumulating and causing harm in the body is highly unlikely (Nabi.S, 2014). Moreover, in 1999 the American Academy of Paediatrics stipulated the removal of Thimerosal from vaccines as a precautionary step, nullifying the whole argument. 

Present-day research

Although studies have failed to show any substantial proof linking MMR and Thimerosal with autism, modern research is focusing on other vaccines.

Research suggests that glutamate receptor dysfunction can result in mental disorders like autism

This includes the Pandemrix vaccine, which is said to induce GR (glutamate receptor) antibodies in the body that can cause the loss of GR receptors, responsible for the body's immune response (Arumugham 2019). Subsequently, GR dysfunction can result in mental disorders like autism (Rojas, 2014, as cited in Arumugham, 2019).

The study finds that GR antibodies are formed because of plant/animal proteins used for making the vaccines, and then decisively concludes by saying that such proteins should not be used while producing vaccines.

Even though the study provides evidence of a connection between glutamate receptors and autism, a major drawback is that both the main study and the cited study, have no evidence of the exact biological mechanism of how the loss of GR causes autism. Moreover, the results of both the studies have been acquired from insufficient data which can’t be considered representative of the total population.

Hence, even modern research requires large scale studies and further biological advancements. 

It is explicit that the Thimerosal and MMR vaccine hypotheses were rejected because of lack of scientific rigour. However, it is extremely important that scientific research regarding the safety of vaccines take place. But, only those studies which have proof of their biological mechanisms, or are large prospective population studies, should be considered legitimate.

Based on the studies analysed, it can be boldly concluded that there is no link between vaccines and autism; rather, the claim is more of a causal fallacy.

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