Guest post by Dr. Maithili Pai as part of our World Immunization Week awareness campaign.

Dr. Maithili Pai is a dental surgeon, currently pursuing a post-graduate program in pediatric dentistry at the University of California, Los Angeles. She is a Practo Ray user since June 2011.

There have been widespread rumours that vaccinations cause autism, and Dr. Pai debunks this myth for us. 


Do Vaccines Cause Autism? Here’s Exploring an Urban Legend.


There are some things in life that should just be a given. Game of Thrones getting renewed for another season, making fashion designers work with size 14 models, and well, getting kids vaccinated. Though why the second doesn’t happen is a mystery to me, the third being questioned is bewildering more than anything else.

I study in Los Angeles. The hub of all that is glamorous and flaky, trendy and hip, and yes, people here have opinions on everything. Staying here I know what is Kale and Quinoa, and the difference between the two. And if that doesn’t explain it, I don’t know what does.

Anyway, moving to the big immunization debate. It all began with an article that suggested a link between certain vaccines and Autism. Researchers analyzed medical & demographic records to find that the percentage of children with autism had been rising over the years, and linked this data with vaccination trends in the same period. They then concluded that vaccinations could be a cause of this steady increase in autism spectrum disorders.
However, they failed to conclude whether this was due to more cases being diagnosed (as the spectrum of autism disorders was widened), or due to an actual increase in the number of autism-affected patients. But it was irrefutably concluded that there had been a sharp numerical increase in autism spectrum disorder cases.

Interesting, isn’t it? Lets find out more.

What is autism spectrum disorder?

Autism spectrum disorder (ASD) describes a range of conditions classified as neuro-developmental disorders. Published in 2013, the autism spectrum now combines the previous diagnoses of autism, Asperger syndrome, pervasive developmental disorder not otherwise specified (PDD-NOS), childhood disintegrative disorder, and Rett syndrome.

The US has seen a steady and sharp growth in ASD cases in the last few years. Here is a graph to easily understand this:

Autism cases per 1,000 children in the U.S. from 1996 to 2007
Autism cases per 1,000 children in the U.S. from 1996 to 2007

(Specifically, a chart of the number (per 1,000 U.S. resident children aged 6–17) of children aged 6–17 who were served under the Individuals with Disabilities Education Act (IDEA) with a diagnosis of autism, from 1996 through 2007. Sourced from Wikimedia Commons.)

How exactly do vaccines cause autism?

Well they don’t! There is an interesting story behind how this unfounded public perception came to be.

The CDC (Centers for Disease Control and Prevention) is an agency of the US government that aims to protect public health & safety. In 1999, while reviewing mercury-containing food & medicines, the CDC and the American Academy of Pediatrics asked vaccine manufacturers to remove a mercury-based preservative called thiomersal from vaccines purely as a precautionary measure.
Thimerosal was rapidly phased out of most U.S. and European vaccines. Many parents saw this action to remove thiomersal – in the setting of a perceived increasing rate of autism as well as increasing number of vaccines in the childhood vaccination schedule – as indicating that the preservative was the cause of autism.

More about Thimerosal:

Thimerosal (also known as thiomersal and Merthiolate), is an antifungal & antiseptic agent used in vaccines, immunoglobulin preparations, skin test antigens, antivenins, ophthalmic & nasal products and even tattoo inks.
The earliest studies about thimerosal-containing vaccines implicated the MMR vaccine (Measles, Mumps & Rubella), which resulted in a lot of parents avoiding administering this vaccine to their children.

However, several respected studies negate the effects of that study, especially the landmark 2004 literature review (Thimerosal-Containing Vaccines and Autistic Spectrum Disorder: A Critical Review of Published Original Data) which aggregated & analyzed the findings of previous studies about this controversy.

“Studies do not demonstrate a link between thimerosal-containing vaccines and ASD (autism spectrum disorder), and the pharmacokinetics of ethylmercury make such an association less likely. Epidemiological studies that support a link demonstrated significant design flaws that invalidate their conclusions. Evidence does not support a change in the standard of practice with regard to administration of thimerosal-containing vaccines in areas of the world where they are used.”

More recently, a 2012 pilot study in Japan concludes “In this study, there were not any convincing evidences that MMR vaccination and increasing the number of vaccine injections were associated with an increased risk of ASD in a genetically homogeneous population. Therefore, these findings indicate that there is no basis for avoiding vaccination out of concern for ASD.”

To conclude

There may be a barrage of articles, studies and even celebrity endorsements on either sides of this argument, but the fact remains that the benefits of a vaccine far outweigh the risks of the associated disease. Vaccination also reduces the number and severity of complications in the rare instance that the disease occurs even though a vaccine was given in the past.

Earlier this year, there was an outbreak of mumps in New York, and closer home there was an outbreak of measles in California. It was surprising that this happened even though all the vaccines to prevent the disease have been available for years. But once the outbreak happened, believers and skeptics alike lined up to get their children vaccinated, proving that people do know the importance & necessity of vaccination. Why this then continues to be an issue of chatty conversation is a mystery to me.


1. Autism Spectrum Disorder Fact Sheet, American Psychiatric Association, accessed 15 April 2014.
2. Thimerosal-Containing Vaccines and Autistic Spectrum Disorder: A Critical Review of Published Original Data by Parker S. K, Schwartz B, Todd J, Pickering L. K. Pediatrics Vol. 114 No. 3 September 1, 2004. pp. 793 -804 (doi: 10.1542/peds.2004-0434)
3. Mercury, Vaccines, and Autism: One Controversy, Three Histories by Baker JP. Am J Public Health 98 (2): 244–53. (doi:10.2105/AJPH.2007.113159)
4. Thimerosal in vaccines: frequently asked questions (FAQs). Center for Biologics Evaluation and Research, U.S. Food and Drug Administration. 2007-06-07. Retrieved 2008-07-22.
5. Prevalence and changes in diagnostic practice: The prevalence of autism by Fombonne E. JAMA. 2003;289(1):87-9. (doi: 10.1001/jama.289.1.87)
6. The epidemiology of autistic spectrum disorders: is the prevalence rising? by Wing L, Potter D. Ment Retard Dev Disabil Res Rev. 2002;8(3):151–61. (doi:10.1002/mrdd.10029)
7. The combined measles, mumps, and rubella vaccines and the total number of vaccines are not associated with development of autism spectrum disorder: The first case-control study in Asia by Uno Y, Uchiyama T, Sleksic B, Ozaki N. Vaccine. 2012 Jun 13;30(28):4292-8. (doi: 10.1016/j.vaccine.2012.01.093)
8. A two-phase study evaluating the relationship between Thimerosal-containing vaccine administration and the risk for an autism spectrum disorder diagnosis in the United States by Geier DA, Hooker BS, Kern JK, King PG, Sykes LK, Geier MR. Transl Neurodegener. 2013 Dec 19;2(1):25. (doi: 10.1186/2047-9158-2-25)