Written by David Mills and Andrea Rice — Fact checked by Jill Seladi-Schulman, Ph.D.
Vaccines are widely regarded as safe and effective. However, vaccine skepticism and hesitancy have contributed to low childhood vaccination rates in the United States.
A large new study of 1.2 million children found no compelling evidence to suggest that childhood vaccines could cause autism or other chronic health conditions. The findings were published on July 15 in Annals of Internal Medicine.
The 24-year-long study, conducted by Danish researchers, examined the safety of aluminum salts used in vaccines, which Health and Human Services (HHS) Secretary Robert F. Kennedy Jr. has referred to as “neurotoxic.” The longstanding debate over the safety of aluminum among vaccine skeptics has been repeatedly debunked.
As an adjuvant, aluminum has been added to vaccines for more than 70 yearsTrusted Source to improve how the immune system responds to vaccines. The use of adjuvants also allows for smaller doses of a vaccine antigen to be used and for fewer doses of a vaccine to be needed for protection
“It’s really important for parents to understand that we are not injecting metal into children,” senior study author and epidemiologist Anders Hviid of the Statens Serum Institute in Denmark, told NBC News.
“Our study addresses many of these concerns and provides clear and robust evidence for the safety of childhood vaccines,” Hviid added.
Still, scientific consensus over vaccine safety and so-called autism risk remains under question by top health officials, at least in the United States.
Earlier this year, HHS officials, including the Health Secretary, said that the Centers for Disease Control and Prevention (CDC) would investigate whether vaccines cause autism.
“As President Trump said in his Joint Address to Congress, the rate of autism in American children has skyrocketed. CDC will leave no stone unturned in its mission to figure out what exactly is happening,” a department statement said. “The American people expect high quality research and transparency and that is what CDC is delivering.”
Despite what some people may believe, experts say vaccinations help prevent the spread of infectious diseases. They also help protect those who can’t receive them. Most health experts would agree they do not cause autism.
No evidence linking vaccines and autism risk
The new Danish study provides compelling, reassuring evidence over the safety of aluminum used in vaccines.
Experts not affiliated with the research told Healthline that there have been multitudes of reputable studies on vaccine safety in recent decades, and none have found a definitive link to autism.
“The scientific community has researched this very thoroughly and there’s no evidence that childhood vaccines cause autism,” said Danelle Fisher, MD, a pediatrician at Providence Saint John’s Health Center in Santa Monica, CA.
“Scientists from around the world have approached this question in several different ways and none has found a relationship,” added Bryan King, MD, vice chair for child psychiatry and a professor in the school of medicine at the University of California San Francisco. “Scientists have also looked at whether different preservatives in vaccines could have an effect and none exists.”
Experts reaffirmed the importance of children receiving their scheduled vaccinations to prevent infectious and potentially deadly illnesses like measles from spreading. The growing measles outbreak that began in western Texas in January has been linked to low vaccination rates.
“In some ways, we are victims of our success when it comes to vaccines,” King said. “They can be so successful in preventing severe illness and death that we can lose sight of why we need or want to be protected from those potentially devastating diseases. We forget how devastating those diseases are.”
King and other experts noted that vaccinating the majority of children can help protect children who can’t receive vaccines because they are undergoing cancer treatment or have compromised immune systems.
“We need to cocoon these kids,” said Gina Posner, MD, a pediatrician at MemorialCare Medical Group in Fountain Valley, CA.
“It is incumbent upon everyone to be good community members,” added Fisher.
Facts about autism
Autism spectrum disorder (ASD) is a broad term used to describe a group of neurodevelopmental conditions.
The conditions generally affect communication and social interaction. People on the autism spectrum often demonstrate restricted and repetitive interests or patterns of behavior, and language skills are often delayed in children.
The degree to which a person falls on the autism spectrum may vary greatly from person to person. Five subtypes of autism have been identified.
Most people are diagnosed with autism as children, but adults are sometimes diagnosed as well.
Some symptoms of autism may include:
- repetitive movements such as rocking or arm flapping
- lining up objects such as toys in a strict order
- repeating words and phrases over and over again
- becoming upset over minor changes in routines
- delayed movement, language, or cognitive skills
- excessive worry or stress
- unusual levels of fear (either higher or lower than expected)
- hyperactive, inattentive, or impulsive behaviors
- unexpected emotional reactions
- unusual eating habits or preferences
- unusual sleep patterns
- self-stimulating behaviors, known as “stimming“
Experts say early intervention when children are young can help ease symptoms and help autistic people improve their quality of life.
“Early intervention is amazing,” Posner told Healthline. Some early intervention therapies for autism may include:
- discrete trial training to encourage step-by-step learning
- early intensive behavior intervention with one-on-one therapy sessions that help children under 5
- verbal behavioral interventions
- positive behavior support
- cognitive behavioral therapy
- social skills training
- sensory integration therapy
- occupational therapy
- speech therapy
- medication (i.e., antipsychotics, antidepressants, or stimulants)
How prevalent is autism?
President Donald Trump and HHS Secretary RFK Jr. have quoted figures saying autism rates in the U.S. have skyrocketed from 1 in 10,000 children in 2000 to 1 in 36 children today. The 1 in 10,000 number appears to come from a single study in the 1960s.
The CDC reportsTrusted Source that autism rates have more likely increased from 1 in 150 children in 2000 to 1 in 31 in 2022.
The agency also notes that an autism spectrum disorder is over three times more common in boys than it is in girls.
Experts note they believe the increase in autism rates in the past two decades is due to better diagnosis of the condition. King points out that vaccination rates have not increased in the past 10 years while the rate of autism diagnoses has gone up.
“The rate of autism is as much as it’s always been. Now, it’s just identified better,” Fisher told Healthline.
“A lot of it is we are better at diagnosing,” added Posner.
King added that “the definition of autism now includes a broader spectrum, which may partially explain the increase in prevalence over earlier estimates.”
Possible causes of autism
If vaccines don’t cause autism, then what does?
Experts say there are probably a multitude of factors behind the development of autism, but they say the number one reason is most likely genetics, noting that autism tends to be more common in some families than in others.
In 2023, researchers reported they had identified seven genes linked to an increased risk of autism.
When introducing their research results, they also noted that prior research has estimated that 50% of genetic risk can be predicted by common genetic variation, and another 15% to 20% is due to spontaneous mutations or predictable inheritance patterns.
“None of the hundreds of genes that contribute to the risk for autism is specific, that is, that a so-called autism gene always or only leads to autism,” King told Healthline.
“But these genes disrupt the usual development or function of pathways in the brain in ways that significantly increase autism risk. The timing of these effects begins before birth, so as scientists look for causes of autism, the focus is on genes or environmental exposures that occur long before children are receiving immunizations,” he added.
Experts said that children of older parents tend to have higher autism risks due to the aging of sperm and eggs. A 2020 study determined that children born to older parents have a 50% higher risk of autism.
Posner added there is also evidence that premature infants have higher autism risks, as do children bornTrusted Source to mothers with gestational diabetes.
“You can’t specifically point to one cause,” said Fisher. “No two autistic kids are the same.”
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