Vaccine refusal: a case of toddler logic syndrome

A couple of weeks ago, my family was traveling out of town. I was driving and my wife and almost 2-year-old daughter were buckled up in the back seat playing with some toys. My wife pulled out a brand new container of Play-Doh®. As my daughter was preparing to pull the lid off to see what was inside, I drove through a section on the interstate where there was a very strong, pungent smell of manure. Everyone in the car (including my daughter) in unison said, “Ewwww!!!” and for the rest of the trip, every time she opened her Play-Doh®, she said, “Ewwww!!!” even though the manure odor had long passed.

You see, my daughter truly believed that Play-Doh® smelled like manure. There was no talking her out of it. Even after the stench was gone, she knew that the whiff of dung began when she took the lid off the container. She correctly correlated the awful stink to the timing of the opening of the Play-Doh®, but she incorrectly assigned causation to it. This same flawed “toddler logic” is sometimes used by adults when it comes to assigning causes to certain developmental conditions, especially autism.

Even though many studies have refuted a link between vaccinations and pervasive developmental disorders (i.e., autism) and The Lancet retracted the fraudulent study by Dr. Andrew Wakefield, millions of parents have been duped (often by misinformed celebrities) into believing that vaccines can cause detriment to the health of their children. This is a classic case of toddler logic, where it’s easy to assume that A causes B (that vaccines cause autism) simply because A correlated with B (kids who get vaccines sometimes show symptoms of autism around the same age).

It is much more convenient to just blame vaccines. They are given around the time developmental concerns start to present. The shots are not without pain, are not a pleasant experience, and there’s already a prevailing attitude among Hollywood and even some in the medical community that vaccines could still be possibly linked to autism. Sound evidence to the contrary still doesn’t seem to dispel the myth. In fact, in a survey released by the National Consumers League (NCL) in April 2014, 33 percent of parents of children under the age of 18 and 29 percent of all adults continue to believe “vaccinations can cause autism.”

While being skeptical of correlation resulting in causation is good for scientific inquiry, dismissing correlation entirely, as if it cannot suggest causation at all, can be just as risky. Epidemiologists and statisticians hone in on scientific evidence quite frequently by looking at trends in data. There is still much to be learned about autism and its root cause.

It is second nature for us to hang our hat on a simple cause-effect relationship. We see it all of the time in the real world. Yet we do not see the moving parts behind what it takes to go from A to B. Coincidentally, a patient is vaccinated (in the case of MMR, usually at 12 months of age) and then developmental regression or delay is noted. Parents out of fear, frustration, confusion, or a severe case of toddler logic syndrome (TLS) are deciding to delay or outright refuse vaccines. There’s no wonder there have been multiple recent outbreaks of measles, mumps, and pertussis in the United States.

Note: Toddler Logic Syndrome, or TLS, is not a real medical diagnosis. I totally made it up.

About Dr. Justin Morgan, Bundoo Pediatrician

Justin Morgan, MD, FAAP, is a board-certified pediatrician who practices general pediatrics in Louisville, Kentucky. He cares for children of all ages.


  1. I like your analogy and clarification to parents who are reading your article that correlation of two events does NOT always result in causation. Just because two events occur at the same time, doesn’t mean one caused the other. That’s why scientific experimentation is so extremely important in cases such as this. There is entirely way too much pseudoscience on the subject, and a lot of parents take it as fact without reading between the lines.

    1. Thanks for your comment! I’m glad you enjoyed it.

  2. Luckily, subsequent cans of Play Doh smelled like…Play Doh!

  3. I am shocked (but may be not surprised….) that 33% percent of Americans still think vaccines cause autism. That is much too high! I do love your playdoh analogy (though it will be interesting to see how that plays out for your guys in the future 😉 Note to your family: no playdoh gifts in the Morgan household anytime soon!


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