Updated 24 November 2025
Editorial note: On Wednesday, November 18, 2025, the Centers for Disease Control and Prevention . According to The New York Times:
“On Thursday, the live version of the page stated: ‘The claim ‘vaccines do not cause autism’ is not an evidence-based claim because studies have not ruled out the possibility that infant vaccines cause autism.’
The updated text also claimed that the health authorities have’ignored’ studies supporting a link and said that the Department of Health and Human Services was conducting a ‘comprehensive assessment’ of the causes of autism.”
As a result of these misleading claims on the CDC website, we are updating the article below with authoritative sources on the subject.
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Autism is . It is also known as “Autism Spectrum Disorder,” reflecting the wide range of ways in which autism manifests itself in the general population. Simply put, a person with autism () processes information differently than a person.
An autism diagnosis is based on difficulties with typical social skills, a preference for repetition and routine, communication disabilities (whether verbal or non-verbal), and not meeting developmental milestones. However, it is essential to know that . Therefore, autistic people need understanding and support, not cures or treatments.
Autism prevalence (the number of existing cases) in the United States . Over the decades, bad science and the lack of a scientific approach to autism have fueled conspiracy theories that blame vaccines as the reason for this increase. However, the scientific community has shown that the increase in prevalence is due to several factors. These include better diagnostic tools for detecting autism in children, better access to care (which leads to more diagnoses), and more social acceptance of autism (which means that more parents are likely to share their children’s diagnoses).
While , vaccines are not among those reasons. In fact, the rubella vaccine has been shown to protect against autism. How? The vaccine protects pregnant people from rubella disease, which could cause (CRS) in the unborn. A child born with CRS is likely to show autistic behavior and developmental delays. It is worth noting that the rubella vaccine is combined with the mumps and measles vaccines in the United States as the MMR vaccine.
A Matter of Timing
One of the easiest ways to answer why vaccines were associated with autism to begin with is the age at which childhood vaccines are given, and the age at which autism is usually recognized. In the United States, the recommended vaccine schedule includes several vaccines given between birth and twelve months of age. Coincidentally, signs of a developmental delay are recognized around that same age. Children who should be walking or speaking and are not, are getting vaccines shortly before that diagnosis.
This is a classic case of confusing correlation with causation, a phenomenon epidemiologists call or the . When parents and others see autism diagnoses given after vaccines, they blame the vaccines, even when the two events are unrelated. To determine whether the correlation is just a correlation and nothing else, legitimate, well-conducted scientific studies are needed.
You see, the timing of the autism prevalence estimates is important. Before the 1990s, prevalence was estimated using limited studies in limited places around the United States. Since then, not only have diagnostic criteria changed, but so have the methods and tests available to diagnose autism. So it is not scientifically proper to compare current estimates based on modern science with estimates done when autism was not well understood, or when society did not count or recognize autistic individuals.
The Wakefield Study on MMR and Autism
The alleged link between autism and vaccines was solidified when Andrew Jeremy Wakefield and colleagues published a now-retracted article in The Lancet. In , Wakefield et al proposed a new syndrome that explained autism appearing after the MMR vaccine given at 12 months. Among the many problems the study had, it lacked a control or comparison group of unvaccinated children. And the study only examined 12 children.
In the article’s discussion section, the authors clearly state: “We did not prove an association between measles, mumps, and rubella vaccine and the syndrome described.” Yet this paper keeps being held up by anti-vaccine groups and individuals as definitive proof that the MMR vaccine causes autism.
Furthermore, investigative journalist Brian Deer discovered that patient records were altered, that Mr. Wakefield was paid to find something wrong with the MMR vaccine, and that Mr. Wakefield was looking to patent his own measles vaccine. , which exposes how Wakefield et al. started a global health scare that continues to this day.
Mr. Deer’s investigation also revealed that most of the children in the study did not fit the profile described in the study. Some had preexisting developmental issues, while others showed symptoms unrelated to the vaccine. The misrepresentation of these children’s cases, together with Mr. Wakefield’s undisclosed financial conflict of interest, led to his removal from the UK medical register along with others on the study’s team. This means they cannot legally practice medicine in the United Kingdom.
Although the scandal discredited Mr. Wakefield as a physician, the damage to public confidence in the MMR vaccine was done. The article and subsequent media appearances by Mr. Wakefield ignited a worldwide vaccine scare that resulted in declining vaccination rates. That translated to outbreaks of measles and other vaccine-preventable diseases. To this day, Mr. Wakefield has a following among some who oppose vaccinations.
The Wakefield “fraud,” , serves as a cautionary tale about the importance of ethical conduct and thorough peer review in medical research. Studies with proper control groups, proper sample sizes, and strict oversight and analysis .
Turning to Thimerosal
Thimerosal is a preservative that has been used in vaccines since the 1930s to prevent bacterial contamination in multi-dose vials. , a mercury-based compound that is rapidly processed and eliminated by the human body. This distinction is critical: ethylmercury is not the same as methylmercury, the form of mercury associated with toxicity from environmental exposure, such as contaminated fish or water. A helpful comparison is ethanol (alcohol found in beverages) versus methanol (a toxic compound that can cause blindness or death if ingested).
The use of thimerosal in medical products spans nearly a century, providing an extensive safety record. However, in the late 1990s and early 2000s, , who suggested a possible link between mercury exposure from thimerosal-containing vaccines (TCVs) and autism spectrum disorders (ASD).
In response to these concerns, a substantial body of scientific research has examined the issue. . For example, a population-based study in Poland found no association after adjusting for potential confounders.
Similarly, . Animal studies, including those involving infant rhesus macaques, also failed to demonstrate any autism-like behaviors or neuropathology following thimerosal exposure.
Despite the absence of evidence supporting a causal link, public concern persisted. As a precautionary measure and to maintain public confidence in vaccines, . Some influenza vaccines in multi-dose vials still contain thimerosal, but its use is limited.
Importantly, autism prevalence has continued to rise since thimerosal was removed from most vaccines, further undermining the hypothesis of a causal link. .
If Not Vaccines, Then What?
The observed increase in autism diagnoses over the past two decades is likely due to improved recognition, broader diagnostic criteria, and greater public awareness—not a true increase in incidence. Current scientific consensus suggests that autism is a neurodevelopmental condition with a complex etiology, likely involving a combination of genetic and environmental factors in a small subset of cases.
However, for most individuals, autism is increasingly understood as a natural variation in brain development. Further research is needed to fully characterize the contributing factors and their interactions, which may in turn improve early identification, access to services, and targeted support for individuals on the autism spectrum.
Conclusion
Autism is a complex disorder that presents itself in many ways in different people. Some people will be affected greatly, needing constant care and support services throughout their lives. Others will be affected minimally, requiring only a few accommodations. In any case, it is important to emphasize that people with autism still have feelings, hopes, and dreams, just like anyone else. It’s just that their interface with the world – their brain – functions differently than most people. The resources spent on chasing a cause already disproved could be better spent on services for autistic individuals and their caretakers.
Additional Information and Resources
- Autism Self Advocacy Network:
- Center for Autism Spectrum Disorders at Children’s National Hospital:
- Autism Integrated Care Program at Children's Hospital of Philadelphia: