You are an educated reader, so I know that you know that vaccines do not cause autism. However, you probably have also read headlines such as the recent U.S. Health and Human Services release, “Autism Epidemic Runs Rampant.”
Is there an epidemic-level increase in autism rates? Are vaccines involved in any way?
Autism spectrum disorder (ASD) diagnoses have multiplied. Successive editions of my introductory psychology texts have offered updated Centers for Disease Control and Prevention estimates of U.S. childhood autism rates:
- My ninth edition, published in 2009, reported that 1 in 150 children were diagnosed.
- Tenth edition (2012): 1 in 110
- Eleventh edition (2014): 1 in 68
- Twelfth edition (2020): 1 in 59
- Fourteenth edition (2023): 1 in 54
- Briefer edition (2024): 1 in 38
- Briefest edition (2025): 1 in 31
There are at least two possible contributors to a genuine autism increase. Premature babies more often get diagnosed with autism, and with medical advances today’s preemies more often survive to experience childhood. Also, older parents more often give birth to children with autism, so the increasing age of birthing parents may contribute.
But other possibilities seemingly explain most of the increased autism reporting:
- Relabeling of children’s disorders. Increased ASD diagnoses have been partly offset by a decrease in children diagnosed with “cognitive disability” or “learning disability.”
- Better detection. The quintupled rate of autism diagnoses since 2009 also results from increased awareness and early autism detection—rather like breast cancer diagnoses increasing during the 1980s thanks to mammography adoption.
- Expanded labeling. Broadened criteria for ASD diagnosis may have led to some “concept creep.” With more clinicians trained in early detection, children are being diagnosed today who might earlier have just been considered a bit different. If growing up today, Bill Gates believes he would have been diagnosed with ASD. He reports that, as a child, he was “obsessed with certain projects, missed social cues and could be rude or inappropriate without seeming to notice his effect on others.” As an interviewer noted, “He still rocks back and forth like a metronome as he talks [and] thinks his superpower is his neurodiversity and ability to hyperfocus—he can remember all the number plates of his first employees.”
So, to answer my first question, there does appear to be some actual autism increase, though the bigger contributor is likely more liberal diagnosing of children.
Now to my second question: What causes autism, and might vaccines be even a small contributor?
Vaccines do not cause autism. However, the subtle power of repetition (“vaccines cause autism”) seems to have caused many people to wonder if increased childhood vaccinations partially contribute to an “autism epidemic.” If you are unsure, you have much company, as evident from a 2025 KFF U.S survey:
Children receive a measles/mumps/rubella (MMR) vaccination in early childhood, about the time ASD symptoms first get noticed. So, it’s understandable that some parents presumed the vaccination caused the ensuing ASD, an idea that spread after a 1998 British study claimed to have found a vaccine–autism connection. But that anti-vax-inspiring study—“the most damaging medical hoax of the last 100 years”—turned out to be fraudulent. The publication was retracted and its medical author disbarred.
Others have worried that thimerosal, a mercury vaccine preservative, might cause autism. But experts discount that possibility, noting also that childhood vaccines since 2001 have been thimerosal-free. Even so, vaccine doubts and fears persist, contributing to this year’s measles outbreak.
Yet the evidence could not be clearer. Studies of a gazillion children, including one following more than a million, reveal identical autism rates in those vaccinated and unvaccinated. A slight exception was one study that followed nearly 700,000 Danish children: Those receiving the MMR vaccine were slightly less likely to later be among the 6517 ASD-diagnosed children. Moreover, among children diagnosed with autism after vaccinations, family home movies have revealed less eye contact and other early autism symptoms appearing before vaccination.
Although vaccines clearly do not cause autism, other biological factors do. As we document in Psychology, Fourteenth Edition, the prenatal environment can matter, especially when altered by maternal infection, toxins, psychiatric drug use, or stress. But multiple genes matter more. One five-nation study of 2 million people found the heritability of ASD was near 80 percent. If one identical twin is diagnosed with ASD, the chances are about 9 in 10 that the co-twin will be as well, although such twins often differ in symptom severity.
So, is there an autism epidemic? There has definitely been a multiplication of autism spectrum diagnoses, to which in utero biology contributes, though the increase appears to be due more to expansive diagnoses. Regardless, vaccines do not contribute.
And such neurodiversity can have an upside. As the scientist Temple Grandin reportedly explained on behalf of those sharing her autism diagnosis, “The most interesting people you’ll find are ones that don’t fit into your average cardboard box.” Bill Gates would agree: “If they ever invent a pill where they could say, ‘OK, your social skills will be normal, but your ability to concentrate would also be normal,’ I wouldn’t take the pill.”
[June 23, 2025 update: Psychiatrist Allen Frances, who led the task force that created the DSM's expanded definition of ASD, explains here how the changing definition--blurring "the boundary between autism and social awkwardness"--explains the multiplying diagnoses (it's not vaccine related).]
David Myers, a Hope College social psychologist, authors psychology textbooks and trade books, including his recent essay collection, How Do We Know Ourselves? Curiosities and Marvels of the Human Mind.
