Do Vaccines Cause Autism?

Medically Reviewed by Amita Shroff, MD on June 22, 2022
3 min read

The research is clear: Vaccines don’t cause autism. More than a dozen studies have tried to find a link. Each one has come up empty.

The debate began in 1998 when British researchers published a paper stating that the measles-mumps-rubella (MMR) vaccine caused autism.

The paper itself later was officially labeled “fraud” by England’s General Medical Counsel, but it triggered a lot of debate over the safety of the vaccine which continues to this day.

The study looked at only 12 children, but it received a lot of publicity because at the same time, there was a rapid increase in the number of kids diagnosed with the condition.

The paper’s findings led other doctors to do their own research into the link between the MMR vaccine and autism. At least 12 follow-up studies were done. None found any evidence the vaccine caused autism.

An investigation into the 1998 study also uncovered a number of problems with how it was conducted. The journal that published it eventually retracted it. That meant the publication no longer stood by the results.

In 2010, the General Medical Counsel declared that the paper was not only based on bad science, but was deliberate fraud and falsifications by the head researcher, Dr. Andrew Wakefield, and revoked his medical license. Investigators learned that a lawyer looking for a link between the vaccine and autism had paid Wakefield more than £435,000 (equal to more than a half-million dollars).

A year after the British study, fears about a possible vaccine-autism link shifted from MMR to a substance used in some children’s vaccines. It was called thimerosal, and it contained mercury. That’s a metal that’s harmful to the brain and kidneys at high levels. Doctors used thimerosal to prevent the growth of bacteria and fungi in vaccines.

There was no evidence that the small amount used in the medicines caused harm. Still, it was taken out of most children’s vaccines by 2001 at the urging of the American Academy of Pediatrics and the U.S. Public Health Service.

To see if thimerosal was linked to autism, researchers studied children who received vaccines that contained it. They compared them to kids who received vaccines that didn’t. The CDC conducted or paid for nine different studies looking at thimerosal and autism. It found no link.

What’s more, autism diagnoses continued to rise after vaccine makers took thimerosal out of almost all childhood vaccines. (Today, trace amounts of it remain in the vaccines to protect against diphtheria, tetanus and pertussis, known as DTaP and DTaP-Hib.)

Researchers have also looked to see if all the vaccines required before age 2 somehow together triggered autism. Children receive 25 shots in the first 15 months of life. Some people feared that getting all those shots so early in life could lead to the development of autism, but there is no evidence that this is true.

But the CDC compared groups of children who received vaccines on the recommended schedule and those whose vaccines were delayed or didn’t get them at all. There was no difference in the autism rate between the two groups.

In 2004, the Immunization Safety Review Committee of the Institute of Medicine published a report on the topic. The group looked at all the studies on vaccines and autism, both published and unpublished. It released a 200-page report stating there was no evidence to support a link between vaccines and autism.

Still, studies continue to look at the issue. In 2019, the largest study to date looked at almost 660-thousand children over a course of 11 years and found no link between the vaccine and autism.