The nation’s top health official is promising to determine by this fall why autism rates have surged in recent decades.

In a cabinet meeting Thursday, U.S. Secretary of Health and Human Services said that his agency is working to find out what’s behind the rapid rise in prevalence of the developmental disability and he committed to an ambitious deadline to reach a conclusion.

“We have launched a massive testing and research effort that’s gonna involve hundreds of scientists from around the world,” Kennedy told President Donald Trump and other top federal officials. “By September we will know what has caused the autism epidemic and we’ll be able to eliminate those exposures.”

Autism rates have risen from 1 in 150 U.S. kids in the year 2000 to 1 in 36 currently, according to the Centers for Disease Control and Prevention. Kennedy said at the cabinet meeting that he expects the rate to increase to 1 in 31.

“There will be no bigger news conference than that, if you can come up with that answer,” Trump said in response to Kennedy’s pledge to pinpoint the cause. “Where you stop taking something, you stop eating something or maybe it’s a shot, but something’s causing it.”

Experts attribute the jump in autism prevalence to better awareness, improved screening tools and methods and changes in the diagnostic criteria.

“There are many causes of autism,” according to Autism Speaks. “Research suggests that autism spectrum disorder (ASD) develops from a combination of: genetic influences and environmental influences, including social determinants.”

Kennedy, however, has spent years promoting a link between autism and vaccines despite numerous studies discrediting that theory. During his confirmation hearing to lead HHS, he refused to disavow such views.

More recently, under Kennedy’s leadership, HHS said that the CDC is planning a large study examining the connection between autism and vaccines. The Washington Post reports that the agency has tapped vaccine skeptic David Geier to lead the study. Geier, who has been disciplined by the state of Maryland for practicing medicine without a license, and his father have published papers claiming an association between vaccines and autism, according to the newspaper.

National autism advocacy groups including Autism Speaks, the Autism Society of America, the Autistic Self Advocacy Network and the Autism Science Foundation have all asserted that vaccines do not cause autism.

“RFK Jr.’s comment is a clear signal that HHS intends to produce rigged and fraudulent research that supports Kennedy and Trump’s pre-existing beliefs in a connection between autism and vaccines,” the Autistic Self Advocacy Network said in a statement.

“It seems quite clear that he is forging ahead with rushing out misinformation to the public about the supposed causes of autism,” said Colin Killick, the nonprofit’s executive director, who called the timeline Kennedy is proposing “far too fast for any genuine scientific research to be conducted.”