Above: Image © istockphoto.com/sdominick

Thanks to vaccines, smallpox has been completely eradicated, polio has been eliminated in most countries, and measles is rarely seen in North America.

Did you know? Autism is a devastating disorder that often manifests itself as impaired communication and social skills, as well as a tendency to exhibit repetitive behaviours.

Of course, as with any medical treatment, there are some risks associated with vaccines. Side-effects range from fever and mild rash to serious allergic reactions and seizures. However, such complications are extremely rare. In the United States, there were 1.9 billion vaccines administered between 1991 and 2001. During that time, problems occurred in less than 0.001% of cases.

Autism concerns

Nevertheless, there is still widespread public concern over the safety of vaccines. These concerns can largely be traced to flawed studies that have linked vaccination to a higher risk of autism. In particular, a 1998 paper by British medical researcher Andrew Wakefield linked the measles, mumps and rubella (MMR) vaccine to autism and bowel disease.

Wakefield’s study was eventually found to be fraudulent and it was withdrawn. The author had deliberately altered patient medical histories and data in order to support his claims. For example, he reported that children developed symptoms of autism after receiving the MMR vaccine when medical records indicate that the children began exhibiting symptoms prior to receiving the vaccine.

Currently, medical researchers don’t know what causes autism. However, there is no evidence that vaccines cause the disorder. In fact, a study published in 2013 that took into account the medical histories of 1.3 million children shows that those who have been vaccinated do not have an increased risk of developing autism.

Nevertheless, Wakefield’s study gave important legitimacy to the anti-vaccination movement, contributing to a significant drop in MMR vaccination rates in North America and Europe. In turn, lower vaccination rates have been blamed for recent and sometimes deadly outbreaks of diseases like measles.

Evaluating evidence

When evaluating scientific claims, like those suggesting that vaccines cause autism, it is always important to evaluate the credibility of the data being used to back them up.

Did you know? North and South America, Europe and China are some of the regions that have been declared polio-free thanks to vaccines.

The first line of defence for scientific evidence is peer review, which means that other experts review and critique an article before publication. This helps identify any flaws in the research. However, peer review is not perfect. After all, Wakefield’s article in The Lancet was peer reviewed and the problems with his research and conclusions were only discovered after publication. So even in the case of peer-reviewed studies, both scientists and the general public need to critically evaluate the information.

Scientific studies usually rely on statistical analysis of a sample. It is simply not realistic for researchers to look at every single case, so they will base their study on a certain number of cases that are as representative as possible. For example, it would be impossible to study every single person who has ever received a vaccine. Instead, scientists will study a certain number of cases that will reflect, as much as possible, the broader population.

When evaluating a scientific study, especially if it relies on statistical analysis and sampling, there are three key things to keep in mind:

  • Sample size: In general, the larger the sample, the more representative it will be. To date, any results that suggest vaccines are harmful come from studies with very small sample sizes. For example, Wakefield’s study only looked at 12 children, compared to the 1.3 million cases in the study mentioned above.

  • Experimental design: A badly designed experiment will probably yield inaccurate results. In particular, a carefully designed study will avoid selecting cases in such a way that the sample does not reflect the general population. For example, vaccines can be dangerous for people with weakened immune systems. So any study on the safety of vaccines for the general population needs to be careful that individuals with weakened immune systems are not overrepresented in their sample.

  • Bias: Personal bias and ulterior motives can lead to bad research and even unethical conduct. Researchers may unconsciously or consciously design their experiment to favour one outcome over another. It is essential that scientists declare and readers be aware of any relevant biases or conflicts of interest. For example, Wakefield failed to disclose that he received financial compensation from lawyers planning a lawsuit against vaccine manufacturers. Had the original peer reviewers been aware of this fact, they might have approached the findings more critically and identified the problems with the study before it was published.

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Although autism can be a devastating condition, no credible link has ever been established between receiving any vaccine and developing autism. In fact, vaccines are a safe and essential way of preventing disease and death.

Learn more!

Online resources

The History of Vaccines (2014)
The College of Physicians of Philadelphia

“The History of Vaccines explores the role of immunization in the human experience and examines its continuing contributions to public health.” Resources available on the website include timelines, activities, articles on subjects like disease eradication, and image galleries.

Vaccination greatly reduces disease, disability, death and inequity worldwide (2008)
FE Andre et al., Bulletin of the World Health Organization 86(2), 81-160

A discussion of the benefits of vaccination from a global perspective.

Possible Side-effects from Vaccines (2014)
US Centers for Disease Control

A list of side effects associated with different vaccines, including MMR.

What is a vaccination and how does it work? (2014)
Public Health Agency of Canada

Answers to frequently asked questions about immunization.

What Would Happen If We Stopped Vaccinations? (2014)
US Centers for Disease Control

A discussion of the dangers associated with low vaccination rates.

Wakefield’s article linking MMR vaccine and autism was fraudulent (2011)
Fiona Godlee, Jane Smith and Harvey Marcovitch, BMJ 342

A discussion of Andrew Wakefield’s fraudulent research on a link between vaccines and autism. The authors conclude that, “Clear evidence of falsification of data should now close the door on this damaging vaccine scare.”

Reports on a 2014 measles outbreak in British Columbia.

Scientific Method (2014)

“A beginners guide on key concepts of the Scientific Method, Science, Research and Experiments.”

Other resources

“A beginners guide on key concepts of the Scientific Method, Science, Research and Experiments.”

A retraction of the article published by Andrew Wakefield 12 years earlier in the same journal. A brief introduction is available on the journal’s website. However, a subscription is required to view the full text.

Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies. (2014)
Luke E. Taylor, Amy L. Swerdfeger, Guy D. Eslick. Vaccine 32(29), 3623–3629.

A study that takes into account the medical histories of 1.3 million. It concludes that children who have been vaccinated do not have an increased risk of developing autism. An abstract is available on the publisher’s website. However, a subscription is required to view the full text.

Chris Pascoe

I recently graduated with my PhD in Experimental Medicine from UBC. My research focused on asthma and airway function. I am currently working as a research associate where I am continuing my research. I love to translate scientific research for everyone to understand.

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