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In the past, some experts worried that vaccination with the MMR vaccine might be linked to your child getting autism. But there isn't any good evidence of this.

Here is some more information about this vaccine and autism.

MMR stands for measles, mumps and rubella (German measles). These are infections that can make your child very sick.

Usually, with the MMR vaccine, your child gets one shot when they about 13 months old and another one when they are between 2 years and 4 years old.

The MMR vaccine protects your child from all three infections.

A study in 1998 raised questions about the MMR vaccine and autism.¹ The researchers thought there might be a link between having the vaccine and getting a problem with your bowels. This bowel problem might cause a kind of autistic spectrum disorder. But in the end, the researchers said that their study didn't prove any such link.

This study was small, with only 12 children. And other researchers said it wasn't done well.² But the study showed up in newspapers and on television. Then some parents decided not to give their children the MMR vaccine.³

It can be hard to prove beyond any doubt that a vaccine is safe. This is because millions of children get vaccines. And some of these children later get diseases. But this doesn't mean the vaccine caused the diseases.

To prove a link between the MMR vaccine and autism, we would need to do a type of study called a randomized controlled trial. In this study, some children would get the vaccine and some wouldn't.

But this study would be hard to do, for several reasons. We know that vaccines help a lot in stopping infections. So it wouldn't be fair to keep some children from getting vaccines. Also, the study would have to go on for many years, to spot any problems that take time to show up.

Other types of studies can give us reliable evidence about the MMR vaccine and autism. Two important types are called cohort studies and case control studies.

• In a cohort study, researchers look at a large group of people, usually many thousands, to see how many get autism. Then they check how many of these people got the MMR vaccine.
• In a case-control study, researchers look at two groups. One group has autism. The other group doesn't. Otherwise, the two groups are very similar. The researchers then check which people had the MMR vaccine.

There have now been many of both of these types of study on the MMR vaccine and autism. One summary of the research looked at 12 of the best of these studies. It found that there wasn't any evidence of a link between the MMR vaccine and autistic spectrum disorder.²

• The number of children given the MMR vaccine who get autism isn't any higher than the number of children not given the vaccine but who get autism.
• The number of children getting autism has not gone up since doctors began giving the MMR vaccine.
• The age when the signs of autism show up is the same for children who get the MMR vaccine and for those who don't. This also suggests the vaccine is not the cause.

A recent high-quality study looked at blood levels of measles virus or antibody in children with autism who'd had the MMR vaccine. The study found that the levels of measles virus or antibody in these children's blood was no higher than in children without autism. This shows that the MMR vaccine doesn't cause problems in the way some doctors thought it might.⁴ You can get single vaccines for measles, mumps and rubella. But there isn't any evidence that these are safer than the combined MMR vaccine. And they haven't been tested as much as the MMR.⁵

Also, the full course of single vaccines involves six injections, instead of two injections with MMR. This means more visits to your doctor and more pain for your child, which probably means some children don't get the full course. It also means your child could get one of these infections while waiting for the next single shot.

In the United States, experts recommend that children get the MMR vaccine instead of the single vaccines for measles, mumps and rubella.⁵

You can find out more about autism and the MMR vaccine on the website of the National Institute of Child Health and Human Development (http://www.nichd.nih.gov/).

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.