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People waiting in line in 1976 for the swine flue vaccine. Photo courtesy of the CDC.

Someone posts a blatant lie on social media that you were swimming naked in Lake Superior. How can you prove that you were actually wearing a bathing suit?

This naked swimming scenario describes a classic problem in science: how do you prove that something that does not exist?

Science addresses this problem by carefully and exhaustively examining the data. Any objective review of the data shows that vaccines do not cause autism.

What is autism?

The Autism Spectrum Disorder (ASD) captures the range of the disease. ASD is a neurodevelopmental disorder where the individual shows persistent and pervasive deficits in social communications and interactions. Restrictive, repetitive patterns of behavior, interests or activities are usually present.

The disorder ranges from mild, where individuals strongly prefer to be alone and do not interact well with others, to severe when the individual requires substantial support to complete activities of daily living (such as eating and dressing).

To provide evidence that vaccines do not cause autism, i.e. proving a negative, epidemiological studies compare the rate of autism in vaccinated and unvaccinated children.

One large study examined more than 1 million children and found an identical rate of autism in vaccinated and unvaccinated children. Another comprehensive review of nearly 15 million children also showed no increase in autism among children specifically vaccinated with the MMR vaccine.

How did the lie that vaccines cause autism start?

The canard began in 1998 when a British physician published a paper in the medical journal Lancet falsely claiming a connection between the Measles, Mumps and Rubella (MMR) vaccine and a new disease, autistic enterocolitis.

Subsequent investigations showed that the data were fabricated and the Lancet  Editor-in-Chief stated the paper was entirely flawed. Serious ethical concerns were raised since the studies in the children had not been approved, and the physician was paid by lawyers that were suing the vaccine manufacturer. The paper was retracted and the physician lost his medical license. He sued the organizations that investigated his work, but he lost those cases and was ordered to pay all of the defendant’s costs.

Since the initial story has been debunked, what other possible links exist between vaccines and autism?
Some vaccines contained thimerosal, a mercury-based preservative. The hypothesis was that the thimerosal caused brain damage resulting in autism.

However, the MMR vaccine never contained thimerosal.

More compelling data showing that thimerosal does not cause autism in any vaccine has been found.
In 2001 thimerosal was removed from all childhood vaccines except the annual flu shot
After removing thimerosal, the rate of autism actually increased, showing that thimerosal does not cause autism.

Despite this evidence, vaccine skeptics point out that a correlation does exists between the increase in cases of autism and the increased number of vaccines.

Does correlation equal causation?

A silly example shows correlation does not equal causation.

Each year increases in ice cream consumption correlate with increases in crime. Clearly eating ice cream does not make one more likely to engage in criminal activity. Warmer weather causes the increase in ice cream consumption and crime.

The increase in autism diagnoses does correlate with the increase in vaccination, but this correlation does not prove causation.

The expansion of the criteria in the autism spectrum disorder increased the number of children diagnosed with this condition. Better health insurance means that more children could be tested and diagnosed with autism. 

Importantly, the number of children with severe autism has not increased since the widespread introduction of vaccines.

What about allegations that doctors have a financial incentive to “push vaccines”?

Medical practices, especially pediatric practices, lose money on vaccines. Buying, storing and administering the vaccines costs more than the reimbursement.

In the American medical system doctors are usually paid more to treat disease than prevent disease. While measles is rare, providing hospital care for a measles-infected child brings in much more money than giving the MMR vaccine.

Let’s recap. The original study that the MMR vaccine caused autism was fraudulent. Thimerosal has never been in the MMR vaccine.

Correlation is not the same as causation and studies with millions of children show that the rate of autism is the same in vaccinated and unvaccinated children.

This scientific evidence allows public health agencies (including the World Health Organization, the American Academy of Pediatrics and the American Medical Association) to declare that vaccines are safe and do not cause autism.

Daniel Remick, M.D. is Professor Emeritus of Pathology & Laboratory Medicine at the Boston University Chobanian and Avedisian School of Medicine and former Chair of that Department. Prior to moving to Boston, he was a Professor of Pathology and Assistant Dean of Admissions at the University of Michigan. His research has been supported by grants from the NIH for more than three decades. Dr. Remick grew up in Duluth and graduated from Central High school in 1971.