No, the Recent Danish Study on MMR and Autism Doesn’t Show That Autism Rates Are Lower in Denmark

Leave it to RFK Jr. and his friends to misunderstand epidemiology, again. This time, they published a blog post by JB Handley stating that CDC should go learn from Denmark when it comes to autism and vaccines. Why? Because a recently-published study using health records from thousands of children in Denmark showed something that got the anti-vaccine people curious. In the blog post, JB Handley (a well-known anti-vaccine guru) writes:

“Here in the U.S. we’re at 1 in 36! Shouldn’t CDC researchers rush to Denmark to figure out why their autism rate is so much lower than ours? For every 1,000 Danish kids, only 10 have autism. But here in the U.S., we have 28 per 1,000, that’s 177% more autism! I thought Paul Offit wanted everyone to believe the autism rate was the same everywhere? What gives?

My own personal theory as to why the Danes have a lower autism rate (and it’s just a theory): they do not give the Hepatitis B vaccine. No kids in this study received that vaccine, and the Chinese recently showed Hep B vaccine causes brain damage in mice. I personally think it’s a huge part of the problem. (The Danes also do not give Rotavirus vaccine or flu vaccine, the much lower vaccination requirement of Danish children versus American children is NOT mentioned anywhere in the study.)”

As usual, Mr. Handley seems to not understand what he is reading. He even posts an image from the study to try and support his point:

If you had no clue of what you were talking about, it would kind of make sense that 6,517 autistic children from a total of 650,943 equals 1% and, thus, the autism prevalence in Denmark is 1%, compared with the United States’ 2.8% 1.7%. But this is not the whole story.

The study mentions the cohort of children they followed:

“657 461 children born in Denmark from 1999 through 31 December 2010, with follow-up from 1 year of age and through 31 August 2013.”

When we talk about autism prevalence, we talk about the number of children (age 0 to 17) who are autistic, divided by the total number of children in the United States at the point in time where we are doing the measurement. As you can imagine, the study had children who are now between 10 and 20 years old. That is, there is a significant number of them who are no longer children, right? Also, there is a significant number of children not included right now: those who are under 10 years of age (born since the study ended).

That’s what those numbers are showing. They’re not showing the entire universe of autistic nor neurotypical children. They’re using a cohort that no longer applies to our current knowledge of autism prevalence in the United States. Heck, the year 2000 estimate for autism prevalence in children in the US was 1 in 150, then 1 in 125 in 2004 and 1 in 110 in 2006.

As is par for the course for anti-vaccine people, Mr. Handley is comparing apples to oranges. And, when it comes to incidence of autism by age cohort, this is what the authors found:

The chart above shows the cumulative incidence of autism. That is, at one year of age, not a lot of the children were diagnosed. By age 14, between 2% (vaccinated) and 2.5% (unvaccinated) children are diagnosed as autistic. Does that number sound familiar? I’ll give you a hint: the autism prevalence in the United States is 2.8% 1.7% (or 1 in 36 59 children). Amazing that Denmark would have autism cumulative incidence that is almost the same as our prevalence. (Cumulative incidence adds the number of children diagnosed over time. Prevalence counts the current number of children diagnosed at one point in time.)

I have a theory on why unvaccinated children have higher autism cumulative incidence over the life of the study, but that’s for a later post. For now, you need to know that, one, Denmark does have similar rates of autism as the United States, contrary to what JB Handley misunderstands (or, if he understands, he misinforms).

Two, Denmark is not like the United States. They’re a more homogenous population. We are very diverse, spanning 320 million people on almost a whole continent, coming from just about every part of the world. As we find out more and more that autism has a strong genetic component, it is worthwhile to understand that our diversity leads to different presentations of autism. As we struggle with equal access to care — something that Denmark and other European nations do successfully — our access to care for children with special needs is different than Denmark’s.

Three, this was a very good study, no matter what the naysayers (i.e. antivaxxers) have to say about it. The researchers had medical records of hundreds of thousands of children. They were able to know if those children were exposed to the MMR vaccine or not, and they were able to see when the children were diagnosed as autistic. The fact that more unvaccinated children were diagnosed as autistic by the time they were 14 is very telling.

One would think that people with the resources like JB Handley and RFK Jr. could afford some basic epidemiology courses, or to hire an epidemiologist. Then again, they keep getting things wrong… And what self-respecting epidemiologist worth their salt would ever want to be part of that?

EDIT: The autism prevalence in the united states is 1 in 59 (1.7%) per the latest data from CDC. I apologize for parroting JB Handley’s assertion of 1 in 36.