Open Google, and type in the phrase, "Do vaccines cause autism?" You'll get back more than 24 million results.

Researchers say autism-related brain structure and growth can be detected during pregnancy , long before a baby gets any vaccines at all. And yet, plenty of people believe that the shots children get lead to changes that influence behavior throughout life.

We'll walk through the concerns one by one, covering the current research in 2020, so families can make an informed choice.

Does the MMR Vaccine Cause Autism?

In 1998, a British gastroenterologist published a study linking autism to the measles, mumps, and rubella (MMR) vaccine. People who believe that the shots cause brain changes in young people often refer to this research, and they draw faulty conclusions from it.

The 1998 study has several, well-researched problems. They include:

  • Small sample size. Only eight children were included, and all of them had stated medical conditions. No "healthy" or control children were included.
  • Biased results. Doctors knew about these children when they tested them. Non-blind research like this entices researchers to look for results that feel true, even if they are not.
  • Poor diagnosis. The researcher stated that gastrointestinal symptoms came before autism symptoms in all children. That was later proven false.
  • Faulty disease mechanism. The researcher proposed that the vaccine could prompt intestinal inflammation. That's been proven false.

Controversy about the paper swirled until 2010, when The Lancet (the publisher of the piece) withdrew the paper. Editors discovered that the lead researcher accepted money from anti-vaccine lawyers, and co-authors disagreed with the paper's conclusions.

In 2011, a journalist dug deeper. He interviewed parents of children in the 1998 study and found evidence that the data was falsified . Some children had symptoms that just didn't match the reports in the original study.

But the myth persists, and it's relatively easy to find photocopies or screenshots of the original research. Parents skim it, not knowing that the results were debunked, and they worry.

Danish researchers tried to put those fears to rest. They dug through more than 657,000 medical records of children born between 1999 and 2010. They looked at:

  • Vaccines. How many got their shots, and how many didn't?
  • Autism diagnosis. How many had confirmed diagnoses?
  • Siblings. If one child had autism, did the other develop the issue?

In five years of follow-up, they found no connection between vaccines and autism. Children who skipped the shots were no less likely to develop problems. Children who got the MMR shot were no more likely to develop autism.

This is one of the largest studies ever performed on the link between MMR vaccines and autism. It's also the most comprehensive, as so many children were included. It should put this theory to rest for good.

Are Other Theories Valid?

Anti-vaccine bloggers are prolific, and when one theory is debunked, others pop up to replace it. Two main criticisms continue to swirl around vaccines and autism, and both are simply untrue.

The remaining two criticisms focus on:

  • Vaccine ingredients. Multi-dose vaccines contain trace amounts of the preservative thimerosal. It's a mercury-based additive that helps preserve vaccine potency.
  • The Centers for Disease Control and Prevention explains that this ingredient has been proven safe in multiple studies. It's found only in multi-dose vials of flu vaccines (not all vaccines). Very concerned parents can ask for flu shots that don't include any thimerosal at all.
  • This concern shouldn't keep parents from accepting core vaccines, including the MMR shot.
  • Vaccine spacing. Some parents worry about children getting too many vaccines at once or about shots that protect against many diseases in one vial. The Autism Science Foundation explains that research on spacing has been extensive. Children who had vaccines spaced far apart had no reduced autism risk.

Why Don't People Believe the Current Research?

The Institute for Vaccine Safety says more than 16 sound, credible, controlled studies on vaccines and autism are available. They all say that the link just doesn't exist. Why don't people believe that?

First-person accounts from former anti-vaxxers hold important clues. People may choose to believe that vaccines cause harm because:

  • It makes blame possible. Some parents find comfort in identifying someone or something that is at fault. If they can blame pharmaceutical companies for changes they see in children, that gives them something to fight against.
  • Parents often feel misunderstood. Parents of children with autism spectrum disorder may explain the child's symptoms for years before testing is offered. They sometimes feel suspicious of doctors and silenced by them. The new knowledge seems to offer power.
  • It seems reasonable. Vaccines are given at the age when autism symptoms first appear. It seems to make reasonable sense to some parents that the two are linked, but there is no connection.

Research language can play a part. Medical professionals don't talk in absolutes. They don't say this "does not cause autism." They might say that "this suggests the vaccine is not to blame." As they explain, research can't prove a negative . And the gaps the words leave behind can make people feel suspicious.

Comprehensive education works. When people know more about how vaccines work and why they just can't cause autism, they spread fewer rumors and sow less fear. But until this education is widespread, confusion may remain.

Because the myth about vaccines and autism persists, researchers continue to study the issue. Study after study has come to the same conclusion: Vaccines don’t cause autism.

Are Vaccines Really Safe?

Parents want their children to feel safe, secure, and healthy. Concerns about vaccines can keep parents from giving children these protective measures. Researchers say parents of children with ASD are more likely to be worried about vaccines than parents of children who don't have ASD.

Here's what all parents should know about vaccines:

  • Vaccines work. The American Academy of Pediatrics says vaccines are 90% to 99% effective in preventing disease. Even when they don't offer full protection, they can keep a child from falling seriously ill after disease exposure.
  • The protection vaccines offer saves lives. Childhood illness can kill or maim your child for life.
  • Vaccines are safe. Vaccines are tested repeatedly before they are released to the public. Manufacturing facilities are tested regularly. It takes years to create a vaccine due to all of these protections.
  • Vaccines make our communities safer. When parents withhold vaccines, many people get sick. In 2010 in California, for example, more than 9,000 cases of whooping cough were diagnosed, and 10 infants who were too young for the vaccine died from the sickness .

Vaccinating your child is safe. It's the right thing to do for the community in which you live. And it protects your child from illnesses that can cause very real harm.

If you have concerns about vaccines, talk with your child's pediatrician. Ask for pamphlets or research you can study at home. Return with more questions, if you have them.

The more you know about the vaccine, the better. But don't let myths and biases keep your child from protection that is needed.

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