If your autistic child was vaccinated, you might wonder whether the vaccine caused the autism. Research indicates that the two are not connected.

Autism is a neurodevelopmental difference usually present at birth, before vaccination begins. But the signs may not be noticeable right away.

Many children aren’t diagnosed with autism until they’re about 2 years old. Some people are older — even adult — when they receive their diagnosis.

Autism is identified more now than ever, mostly because of greater awareness and improved screening methods. About 1 in 54 children are autistic.

At one time, many parents believed that childhood vaccines could cause autism. Since then, there has been an abundance of research done that shows otherwise.

A 2014 meta-analysis of 10 studies involving 1,266,327 children showed no relationship between autism and vaccinations. The same analysis also concluded that there is no connection between autism and:

  • MMR: a combination vaccine for measles, mumps, and rubella
  • thimerosal: a vaccine preservative to prevent bacterial growth, used only in multidose vials
  • mercury: a naturally occurring metal found in thimerosal

A Danish MMR vaccine study involving 6,517 autistic children included subgroups for autism risk factors. The results support that:

  • MMR vaccines don’t cause autism
  • MMR vaccines don’t trigger autism in children who are susceptible
  • MMR vaccines aren’t associated with post-vaccination autism clusters

A Japanese study with 413 participants (189 autistic and 224 non-autistic) revealed the same result, showing no convincing evidence that autism onset was linked to the MMR vaccine.

There is also no evidence that the COVID-19 vaccines are linked to autism.

In 1998, British physician Andrew Wakefield and colleagues published a study in The Lancet, a high-profile medical journal. The study proposed a link between the MMR vaccine and increasing rates of autism diagnoses in British children.

Wakefield’s study included only 12 children, was poorly designed, and speculative in nature. Even so, vaccination rates dropped as publicity increased. The idea that vaccines cause autism was easy for parents to believe since vaccination and the appearance of autism signs both occur early in childhood.

Wakefield’s paper was eventually discredited due to:

  • significant procedural errors
  • ethical violations
  • financial conflicts of interest that were not disclosed

The Lancet retracted the paper in February 2010. Wakefield and his co-authors were found guilty of fraud for biased data selection and falsification of facts.

Since then, researchers have continued to look for a link between vaccines and autism but haven’t found one. Despite the availability of studies showing that vaccination doesn’t cause autism, some people continue to believe there is a connection.

Many factors increase a child’s chance of being born with autism.


It’s the opinion of many experts that genetics is the main reason people are autistic.

The heritability of this neurotype ranges from 40% to 80%, with the involvement of multiple genes. For example, having one autistic child increases the likelihood of having a second.

Scientists look at several aspects when assessing genetics:

  • genes: small building blocks that contain instructions for creating proteins
  • chromosomes: a group of many genes, from hundreds to thousands
  • karyotype: a person’s collection of chromosomes, or the process lab technicians use to see chromosomes

Individual gene differences and their combinations with other genes can produce various results, such as:

  • the chance of an autism diagnosis
  • the types of behavioral differences present
  • the level of support the individual might want or need

Changes in chromosomes can result in conditions that sometimes occur with autism, such as:

Karyotypes can reveal the genetic differences of some conditions that occur with autism. An example is Down syndrome, which features an extra copy of chromosome 21 and is visible via karyotyping.

Doctors use karyotyping to identify chromosomal differences. But changes to the many individual genes inside chromosomes may be harder to find. Therefore, a person can be autistic even with a standard karyotype.


About 40% to 50% of autism differences may be influenced by environmental factors. These often occur before or during birth. Some examples include:

  • advanced paternal (father) age
  • young maternal (mother) age
  • birth complications involving reduced blood flow and oxygen to the fetus
  • maternal obesity
  • maternal diabetes
  • caesarian delivery
  • vitamin D deficiency
  • prenatal and infant pesticides exposure

Immune dysfunction

Immune system activity is both environmental and biological because it can happen in both the mother and the infant, before birth (prenatal) and after birth (postnatal).


  • maternal infection that activates an immune response and can cause autism in the fetus
  • maternal anti-brain autoantibodies that result in a subtype of autism


  • immune dysregulation and inflammation in the fetus
  • infant brain changes caused by the infant’s immune system (endogenous anti-brain autoantibodies)

Autism is a spectrum with a wide variety of behavioral differences stemming from many causes. Decades of research have ruled out vaccines as being one of those causes.

If you have a vaccinated autistic child, it’s important to remember that the vaccine isn’t the cause of your child’s autism.

It’s also important not to let your child’s autism factor into the decision of whether to vaccinate younger siblings. If a younger sibling is also autistic, it’s likely due to a genetic factor, and the autism would occur even without vaccination.

It’s estimated that full siblings of autistic children are 20 times more likely also to have autism than siblings of typically developing children, regardless of vaccine status.

Your family doctor can answer any questions about childhood vaccines. The Centers for Disease Control and Prevention (CDC) also has vaccine safety information on its website.