Science shows vaccines do not cause autism

After the United Kingdom General Medical Council described the actions of Andrew Wakefield, MD, author of a 1998 study that erroneously linked vaccinations to autism, as “dishonest and irresponsible,” The Lancet, a respected medical journal, did something it has rarely done in its nearly 200 year history: In 2010, it retracted Wakefield’s article from the published record, publicly acknowledging that the study had no place in any science-based discussion of vaccine safety or autism.

In 1998, Wakefield and his co-authors ignited a firestorm of controversy when they claimed to have found a possible link between autism and the measles-mumps-rubella (MMR) vaccine. Parents fearing that their children would become autistic, refused to have them vaccinated. Lawyers, eager to place blame, filed class action lawsuits. 

A series of articles by journalist Brian Deer later showed the extent of Wakefield’s fraud and how it was perpetrated. Drawing on interviews, documents, and data made public at the General Medical Council hearings, Deer showed how Wakefield altered numerous facts about the patients’ medical histories in order to support his claim; how the Royal Free Hospital and Medical School in London supported Wakefield in his efforts to capitalize on the ensuing fear.

Countless research dollars have since been spent on studies to refute Wakefield’s erroneous findings as more children go unvaccinated and fears of a reemergence of diseases like measles and whooping cough are being realized.

Most recently, one of the largest ever studies of the MMR vaccine evaluated 657,461 children born in Denmark and found no evidence that the MMR vaccine increases the risk of autism. Among the children included in the analysis, 6,517 were diagnosed with autism over the decade-long study period but there was no increased risk among those who received the MMR vaccine when compared to those who had not gotten the vaccine. Nor did the timing of autism diagnoses cluster after the MMR vaccination. These findings provide powerful evidence supporting the safety of the vaccine.

What is autism? 

Autism Spectrum Disorders (ASD) are a group of developmental disabilities that are caused by an abnormality in the brain. According to the Centers for Disease Control and Prevention (CDC), about 1 in 59 U.S. children have ASD. It's diagnosed in nearly 5 times as many boys as girls, and ranges from a severe form to a mild form, known as Asperger syndrome. (Learn more about early signs of autism here.)

Genetics is thought to play a key role in the development of autism. Using a broad definition of autism, when one identical twin has autism, then the other will be affected about 36–95 percent of the time. In fraternal twins, if one child has ASD, the other is affected about 0–31 percent of the time. 

Scientists at the University of California Davis’ M.I.N.D. Institute are also investigating whether environmental exposure to chemicals, pesticides, and metals during pregnancy can lead to autism. 

No link between thimerosal-containing vaccines and autism 

In 2000, in response to a request from the CDC and the National Institutes of Health (NIH), the Institute of Medicine (IOM) established an independent expert committee to evaluate the data and determine whether vaccines cause specific health problems.

The Immunization Safety Review Committee published a series of reports between 2001 and 2004. The committee concluded that neither thimerosal-containing vaccines nor the MMR vaccine is associated with autism. 

According to the CDC, measles, mumps, and rubella (MMR) vaccines do not and never did contain thimerosal. Varicella (chickenpox), inactivated polio (IPV), and pneumococcal conjugate vaccines have also never contained thimerosal. Influenza (flu) vaccines are currently available in both thimerosal-containing (for multi-dose vaccine vials) and thimerosal-free versions. However, in the U.S., most people receive their flu vaccinations from single-use vials, which do not contain thimerosal.

For a complete list of vaccines and their thimerosal content level, see the U.S. Food and Drug Administration (FDA) Thimerosal in Vaccines page.

Are vaccines safe? 

Vaccines have significantly reduced, and in some cases eliminated, many childhood diseases. In the past, polio, rubella, measles, diphtheria, tetanus, chickenpox, and pertussis (whooping cough) were among the diseases that caused thousands of deaths each year. Today, as a result of immunizations, these diseases are rarely seen.

Any discussion of vaccine safety must include a discussion of the benefits of immunizations as well as the risks. All vaccines have possible side effects. Most side effects are mild and include fever, rash, and tenderness or swelling at the injection site. Some side effects can be severe. For example, the pertussis vaccine can cause persistent crying, high fever, and seizures. While these side effects seldom cause permanent damage, they can be frightening for parents. But if you compare the potential risks of vaccines and the established risks of disease, vaccines, with few exceptions, are the safer choice for both children and adults. 

What parents need to know: 

  • Few things in medicine work 100 percent of the time. 
  • Few things in medicine are risk-free. 
  • Researchers are working continually to improve the safety of immunizations. 
  • A decline in immunization rates will lead to an increase in disease.

The only time it is safe to stop giving immunizations is when a disease has been eradicated worldwide.

Last updated April 22, 2019

Suggested Reads