For followers of medical disinformation, the claim that autism is linked to childhood vaccinations is the reddest of red flags. The issue is among the most intensively studied in the scientific literature, and the results among the most conclusive: There's no connection.
That's why the revision by the Centers for Disease Control and Prevention of its advisory on vaccines and autism struck like a thunderbolt, and not in a good way. The original statement was this:
"Studies have shown that there is no link between receiving vaccines and developing autism spectrum disorder ... No links have been found between any vaccine ingredients and ASD."
As of last week, the statement says: "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."
One can't say that the change was a bolt from the blue, because Health and Human Services Secretary Robert F. Kennedy Jr. has telegraphed his intention to revisit the causes of autism for months. The change in the CDC language is merely the most concrete indication that his campaign against child immunizations is undermining the science of public health.
But there is much more to be concerned about.
I've been reporting on RFK Jr.'s assault on public health since his name first surfaced as a possible cabinet appointee in President Donald Trump's second term. Since taking office, Kennedy summarily fired the 17 public members of the CDC's authoritative Advisory Committee on Immunization Practices, replacing its cadre of experienced physicians and vaccine experts with a collection of established antivaxxers and others without detectable scientific expertise.
The harvest of that change was an inaugural meeting of the new panel that was enveloped in a miasma of confused, uninformed debate.
Kennedy appointed a proponent of the discredited claim connecting vaccines and autism to oversee a study of the purported link. He and Trump tried to associate autism among children with their mothers having taken Tylenol during pregnancy—and even associating autism with circumcision. (There's no scientifically validated evidence for those conjectures.)
In April, at his first news conference since taking office, Kennedy spouted a fountain of misinformation about autism. He called it an "epidemic" that is "running rampant," which is untrue. He said "most cases now are severe," which is untrue. In fact the vast majority of new cases involve children without the intellectual disabilities often associated with stereotypical autistic behavior, such as sensitivities to touch and an absence of verbal skills. The prevalence of more severe cases actually has declined in recent years, according to a study from Rutgers.
Kennedy consistently has cited statistics pointing to years of increased autism prevalence, as reflected in ever larger diagnoses, suggesting they point to an "epidemic" of autism and blaming childhood vaccines as a likely factor.
Yet as I've reported, researchers have made great strides in unearthing the causes and characteristics of autism. Among other factors, they've identified genetic anomalies that may produce a predisposition to the condition. Scientific research has absolved vaccines as a cause.
Autism also has been defined ever more broadly over the years — indeed, it's seen today as a smorgasbord of conditions summed up as "autism spectrum disorder. " Despite all that, Kennedy continues to demonize childhood immunization.
The CDC's altered webpage reflects what I've reported as Kennedy's pseudoscientific mindset, relying on claims that have been standard fare for antivaccine activists like himself. Its assertion that "studies have not ruled out the possibility that infant vaccines cause autism" is a travesty of the scientific method.
Science is not well-equipped to prove a negative — as some of Kennedy's critics note, there's no proof that drinking Coca-Cola or eating pizza doesn't cause autism, either.
But by casting doubt on autism research, Kennedy overlooks the research that has been done on vaccines and autism — studies of more than 2 million children around the world, finding no connections whatsoever. Instead, the CDC statement misrepresents some research it does cite, asserting that "approximately one in two surveyed parents of autistic children believe vaccines played a role in their child's autism, often pointing to the vaccines their child received in the first six months of life."
The study the CDC cites for that claim was published in 2006 and was drawn from surveys of 150 parents of children diagnosed with ASD at two private medical practices; the parents were given a six-page, self-administered survey. Only 77 parents responded. Of the respondents, 54% mentioned immunizations as a possible cause of their children's ASD,
The paper was "just about parents' views, not the science of autism," John Harrington, the paper's lead author, told me. "It's definitely not evidence-based in terms of whether vaccines cause autism." The study itself states that its purpose was "to measure parental beliefs and not to measure their accuracy."
I asked Kennedy's agency to comment on this apparent misrepresentation but haven't received a response.
The blast radius from Kennedy's change in the CDC website is vast. The first circle of damage is the possibility that it will encourage more parents to resist immunizations for their children. We already have seen the ramifications from the vaccine hesitancy encourage by Kennedy and his fellow antivaxxers: Reported measles cases in the U.S. reached 1,753 as of Nov. 18, the largest case load since 1991. Other vaccine-preventable diseases such as whooping cough also are on the rise.
The next circle is the CDC's own reputation, which Kennedy has relegated to the dumpster. Once arguably the most trusted public health agency in the world, the CDC has deteriorated into an untrustworthy "propaganda machine for RFK Jr.'s fixed, immutable, science-resistant theories," vaccinologist Paul Offit of Children's Hospital of Philadelphia told researchers at the University of Minnesota. "The CDC is being weaponized to promote RFK Jr.'s antivaccine point of view. So why should you trust it?"
Among those whose reputations are shattered along with the CDC's under Kennedy's onslaught is Sen. Bill Cassidy, R-La., whose vote was a key to confirming him as Health and Human Services secretary. That was because Cassidy, a physician, was skeptical about Kennedy's suitability for the job, but folded his cards when Kennedy made him several promises, including that he wouldn't touch the makeup of the vaccine advisory committee. Cassidy's vote gave Kennedy the majority he needed for confirmation.
Kennedy has broken most of those promises. Last week's breach was the most recent. In announcing his confirmation vote, Cassidy said Kennedy pledged that "the CDC will not remove statements on their website pointing out that vaccines do not cause autism."
Kennedy stuck to that pledge, somewhat — but in a way that arguably intensifies the humiliation he has delivered to Cassidy since the confirmation vote.
The statement "Vaccines do not cause Autism" is still on the CDC website, but it is now accompanied by an asterisk that refers to language asserting that the original statement remains posted "due to an agreement with the chair of the U.S. Senate Health, Education, Labor, and Pensions Committee [that is, Cassidy] that it would remain on the CDC website."
This feels like a shiv aimed at Cassidy: The website undermines the claim that vaccines don't cause autism and says the language remains only because of the promise Kennedy gave to Cassidy and no other. I asked Cassidy's office if the senator took umbrage at the insult but got no reply.
Sunday on CNN, however, Jake Tapper put the issue forthrightly. "Dr. Cassidy," he said, "he lied to you."
Cassidy dodged Tapper's implication, repeating several times that "vaccines are safe" and accusing Tapper of trying to stir up a "titillating" fight between Republicans. As it happens, Kennedy in 2023 launched a campaign for the presidential nomination as a Democrat, the party long identified with Kennedy's family.
Cassidy also posted a tweet Thursday, after the CDC website change, stating, "What parents need to hear right now is vaccines for measles, polio, hepatitis B and other childhood diseases are safe and effective and will not cause autism. Any statement to the contrary is wrong, irresponsible, and actively makes Americans sicker." But he didn't specifically refer to the CDC change or mention Kennedy. I asked Cassidy's spokesperson if he was considering calling for Kennedy to step down but got no reply.
As long as Kennedy remains in place atop the Department of Health and Human Services, the cause of public health in the U.S. and the stature of our public health agencies are at risk, facing the most serious challenges in their history. The American public will be the victim of this campaign of disinformation and pseudoscience.
