A new study published this week in the Journal of the American Medical Association (JAMA) adds to a large body of evidence showing no link between the measles, mumps, and rubella (MMR) vaccine and autism spectrum disorders (ASD). Apart from one study that has since been retracted for falsifying data, there has never been any proven connection between ASD and the MMR vaccine.
Yet misinformation persists and many parents are still wary of vaccines.
The new study looked at the medical records of more than 95,000 children with older siblings, all of whom were enrolled in a large commercial health plan. Siblings of children diagnosed with ASD are known to be at higher risk of autism themselves.
The researchers believed that parents with an autistic child might be more reluctant to vaccinate a sibling and wanted to compare both vaccination rates and rates of ASD diagnoses. They categorized children based on whether their older sibling had been diagnosed with ASD, whether they had ever been diagnosed with ASD, and whether they and/or their sibling had received the MMR vaccine.
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The results showed that parents are less likely to vaccinate siblings of an autistic child—86 percent of the children included in this study were vaccinated at age 5, compared to 92 percent of those children whose sibling did not have ASD.
Vaccination did not affect autism diagnosis even in these higher risk kids. Specifically, 8.6 percent of high-risk kids who weren’t vaccinated were diagnosed with ASD, compared to 3.8 percent of high-risk kids who had received two doses of the MMR vaccine.
In fact, the relative risk of autism among those with older autistic sisters or brothers was lower in those who were vaccinated compared with those who were not vaccinated.
The most important takeaway, however, is that there was no increased risk of autism from the MMR vaccine for any group of kids in the study. For example, among those who did not have an older sibling with ASD, 0.7 percent (or 56 of 7,735 kids) who were not vaccinated were diagnosed with ASD, compared to 0.5 percent (or 244 of 45,578 kids) who were vaccinated.
The authors concluded that “these findings indicate no harmful association between MMR vaccine receipt and ASD even among children already at higher risk for ASD.”
The false connection between vaccines and autism can be traced back to a 1998 study in which British researcher Andrew Wakefield looked at the records of just a dozen autistic children and determined that the MMR vaccine was the cause of their condition.
His complicated explanation—about persistent measles infection of the gut—confused many in the medical community. But having an explanation for the increasing number of ASD diagnoses resonated with parents and trust in vaccines, as well as vaccine rates, plummeted.
Numerous researchers over the next decade tried to recreate his results, with no success. No other study found a connection between autism and vaccines. Wakefield’s study was ultimately retracted and he later lost his medical license when it became clear that there were financial motives behind his vaccine-autism findings.
The authors of the current study hope that their large sample size and the fact that the data was not collected specifically to test vaccine safety (and therefore has no biases) will help put the ghost of Wakefield’s study to rest.
“Even for children who are high-risk, the vaccine does not play a role,” lead author Anjali Jain told Reuters. “We don’t know what does unfortunately, but it’s not the MMR vaccine.”