One of the myths (and there are a lot of them) continually pushed by those opposed to vaccination, is that “the MMR vaccine causes autism” – often coupled with claims that “there are no studies comparing the health of vaccinated & unvaccinated children”. (That’s another myth, by the way.)
The origins of this claim can be laid squarely at the feet of one Andrew Wakefield, who suggested (& has continued to suggest) that the combined measles, mumps, & rubella (MMR) vaccine was linked to the development of autism. This tale of scientific fraud has been well-told elsewhere (see here and here, for example), but the unfortunate result has been a decrease in uptake of the MMR vaccine by some parents and communities, with fairly predictable results. (In fact, ‘vaccine hesitancy’ has been identified by the World Health Organisation as a major threat to public health.)
It’s remarkable that these claims still have legs, given that there is already a significant body of research showing that no such link exists (see here, and here, and here, for example). I’m hoping that a just-released paper by Hviid, Hansen, Frish, & Melbye (2019) will be the final silver nail in that particular coffin. (There’s also quite a weight of evidence indicating a strong genetic component in the development of autism, including the most recent paper on the subject.)
Note that these are not small research studies. In 2002, Madsen & her team published a study based on 537,303 Danish children – yes, more than half a million individuals – covering the period 1991-1998. They concluded that
MMR vaccine was not associated with development of autism and that the risk of autism in the group of vaccinated children was the same as that in unvaccinated children.
Hviid, Hansen, Frish & Melbye’s 2019 study is of a non-overlapping cohort of Danish children ie these children were not included in the earlier Madsen study. It included “all children born in Denmark of Danish-born mothers in the period 1 January 1999 through 31 December 2010”, for a total of 657,461 individuals – probably one of the largest such studies ever undertaken. Children who had other conditions that carried an inherent increased risk of developing autism, such as Präder-Willi syndrome or congenital rubella syndrome, were excluded from the study. Data on vaccination status and autism diagnoses came from nationwide health registries (reporting is mandatory in Denmark), so that the team did not have to rely on parental recall of information.
Of those children, 6,517 were diagnosed with autism during the follow-up period of the study, which ended in 2013. Comparing MMR-vaccinated children with those who hadn’t received the vaccine, the researchers found no increased risk associated with MMR vaccination.
The researchers were also able to examine the risk of developing autism for subgroups of children who were perhaps more likely to do so; for example, those with older siblings already diagnosed with this condition. They found (emphasis mine)
no increased risk for autism in several subgroups: children with a sibling history of autism, children who received other childhood vaccines, or during certain time periods after [receiving a] vaccine.
These findings corroborate the findings of Madsen’s 2002 study; as Hviid et al. say, “the major difference between [these 2 very large studies] is a significant increase in statistical power and additional … analyses.” And it’s worth quoting the conclusions of this latest study (again, my emphasis):
We found no support for the hypothesis of increased risk for autism after MMR vaccination …; no support for the hypothesis of MMR vaccination triggering autism in susceptible subgroups characterised by environmental and familial risk factors; and no support for a clustering of autism cases in specific time periods after MMR vaccination.
You cannot get much clearer than that.