Diseases long thought to be contained are making a comeback, thanks to parents who think that vaccinations harm children. The otherwise childhood utopia of Disneyland saw a major measles outbreak earlier this year, and, in 2014, California declared an epidemic of whooping cough.
The Western United States has been particularly vulnerable to 20th-century diseases, one study from 2013 found, because it is home to dense clusters of anti-vaccination parents in upper-class communities. Though the link between autism and vaccinations has little scientific grounding, some parents seem to see a correlation between the two, and have decided the hedge their bets and not immunize their children.
So, to battle skeptical parents, researchers are re-doubling their efforts to prove that vaccinations are not linked to autism, or any other significant mental issues. A new large-scale study published in the Journal of the American Medical Association shows that there is no association between vaccination and onset autism later in childhood.
In fact, researchers found an extraordinarily large negative correlation: An unvaccinated child could be twice as likely to develop autism later in life. The study analyzed 95,000 children and focused in on those with older siblings with autism spectrum disorders (ASD).
Researchers found an extraordinarily large negative correlation: An unvaccinated child could be twice as likely to develop autism later in life.
Many parents, it seems, think there may be a genetic component that makes some children vulnerable to the adverse effects of the measles, mumps, and rubella (MMR) vaccination. Parents are right that there seems to be a genetic component to the disorder: While the study found that only one percent of children in total had an older sibling with autism, the disorder was approximately seven times more likely to afflict younger siblings in a family where one child already had the disorder.
If there was no association with vaccination and ASD, the researchers should have found no statistically meaningful correlation between the two. But they did find a rather large negative correlation. Ironically, if anything, the latest study would give credence to those who believe that they can "protect" their children from autism by vaccination.
"We believe that the pseudo-'protective' effect is an artifact of selection bias—that parents are not exposing children who are likely to develop ASD (because of increased risk due to a family member or because the child is displaying developmental abnormalities, for example) to the vaccine (reverse causality, in a sense)," Dr. Anjali Jain, co-author on the study, writes an email.
In other words, having an older child with autism may spook parents into not vaccinating future offspring. But, if they were to follow the science, they might actually believe the reverse. "However," Jain continues, "our study did not determine the reason, so that is only speculation. At any rate, we do not actually believe the vaccine protects against ASD."