There’s a question that has reverberated through the last two decades. From a terrified shriek in the early 2000s, to an angry murmur in the following ten years, to the growing calumny it is today, the question has been debated high and low, and studied far and wide.
It goes a little like this: do vaccines cause autism?
Now, we know the answer to this question: it is an emphatic no. There have been studies involving literally millions of children that have failed to find any evidence of an autism-vaccine link. Since 1996 when the question was first raised, to today more than two decades later, there have been hundreds, if not thousands, of studies dedicated to finding even the tiniest increased rate of autism due to vaccines.
They have found nothing. Zip. Nada. The best evidence we have — and it is very, very good — indicates that vaccines don’t cause autism.
And yet, people are still terrified of a link, to the point that vaccine hesitancy/refusal has become a serious concern for the World Health Organisation and is causing measles to reappear all over the world.
Which brings us to the latest study.
Vaccines Don’t Cause Autism
The newest piece of research is a very large study looking at whether the measles, mumps, and rubella (MMR) vaccine caused autism in children in Denmark from 1999 and 2010. Basically, the researchers took Danish children who had the MMR vaccine, and children who didn’t, and compared their risk of later being diagnosed with autism after adjusting for factors like social status and gender.
And when I say “Danish children”, I mean all of them. This study was a spectacular example of what you can do when you have linked data in healthcare — the researchers were able to access the records of every child born in Denmark between 1999 and 2010, which gave them 660,000 people in the study, as well as every single case of autism that was diagnosed in this period.
So what did they find?
Well, in a wonderful twist, the crude analysis in the study found that vaccination reduced a child’s risk of an autism diagnosis by a statistically significant amount. To put it more simply, children who were vaccinated were about 10% less likely to later be diagnosed with autism.
Not what you’d expect if you regularly read conspiracy blogs.
Now, I’m not saying that vaccines reduce your risk of autism. This association disappeared after the study adjusted for social and other factors, which makes perfect sense. It’s almost certain that what’s happening here is that children who are less well-off for one reason or another* are both less likely to get vaccinated, and more likely to be autistic, so the crude analysis is misleading. After adjustment, the relationship totally disappeared, which means that the actual conclusion of the study was that vaccines were not associated with autism in this enormous study.
To put it another way: this study found that vaccines don’t cause autism. Again.
Does this study by itself prove that vaccines don’t cause autism? No. Definitely not. A single observational trial, no matter how big and well-conducted, can’t prove that vaccines are safe. I’ve written about this many times.
This is where context becomes important.
If this was the only study on vaccines and autism, I’d be very cautious about drawing any conclusions from it. But it’s not. We have been studying this question for more than two decades now, and study after study has shown the same thing. Vaccines don’t cause autism, they are not associated with an increased rate of autism, and they’re pretty safe in most other ways too.
Say it with me: vaccines are safe and effective.
Did we really need another study showing the same result? Maybe not. But since there are still thousands of people spreading fear about vaccines online using this flawed link, it certainly doesn’t hurt.
As I’ve said before, I never blame parents for being misled. Having a child is a terrifying roller-coaster. It’s all too easy to be misinformed by people who you think you can trust, and I don’t think anyone should blame parents for sometimes getting it wrong. If you’re worried about vaccines, you should have a talk to your child’s doctor, because ultimately they are the one who knows the entire situation and can give you the best advice.
Just don’t listen to fear-mongering on the internet.
Vaccines don’t cause autism. Full stop.
*I.e. congenital, social, genetic, gender, etc etc etc