President-elect Donald Trump met with Robert Kennedy Jr., a prominent vaccine skeptic, on Tuesday. According to incoming White House press secretary Sean Spicer, the two discussed “the issues pertaining to vaccines and immunizations.”

After the meeting concluded, Kennedy told reporters that Mr. Trump had asked him to “chair a commission on vaccination safety and scientific integrity.” Kennedy said he told Mr. Trump he would chair such a commission, and that their meeting was held at Mr. Trump’s request.

Kennedy, the eldest son of liberal icon Sen. Robert Kennedy, was best known as an environmental advocate before increasingly devoting his time to the supposed dangers of vaccines.

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Mr. Trump has repeatedly shared his belief that there is a link between vaccines and autism.

“I am totally in favor of vaccines,” Mr. Trump said in a 2015 GOP primary debate. “But I want smaller doses over a longer period of time. Same exact amount, but you take this little beautiful baby, and you pump--I mean, it looks just like it’s meant for a horse, not for a child, and we’ve had so many instances, people that work for me. ... [in which] a child, a beautiful child went to have the vaccine, and came back and a week later had a tremendous fever, got very, very sick, now is autistic.”

He also also tweeted about the issue multiple times:

Healthy young child goes to doctor, gets pumped with massive shot of many vaccines, doesn't feel good and changes - AUTISM. Many such cases! — Donald J. Trump (@realDonaldTrump) March 28, 2014

Lots of autism and vaccine response. Stop these massive doses immediately. Go back to single, spread out shots! What do we have to lose. — Donald J. Trump (@realDonaldTrump) October 22, 2012

Kennedy has argued that vaccines, specifically those containing the element thimerosal, may cause autism, a view unsupported by scientific evidence and dismissed as a conspiracy theory by experts.

“Research does not show any link between thimerosal in vaccines and autism, a neurodevelopmental disorder,” says the Center for Disease Control on its website. Moreover, studies linking vaccines and autism have been repeatedly been debunked and discredited, although many parents continue to insist that their children were damaged by immunizations.

Kennedy, who criticized Mr. Trump during the election campaign, has also written a book and promoted a documentary on the subject. During one showing of that documentary, according to the Sacramento Bee, Kennedy compared the damage done by vaccines to “a holocaust.”

“They get the shot, that night they have a fever of a hundred and three, they go to sleep, and three months later their brain is gone,” Kennedy said at the screening in 2015. “This is a holocaust, what this is doing to our country.” It was a comment which he later apologized for, saying, “I employed the term during an impromptu speech as I struggled to find an expression to convey the catastrophic tragedy of autism which has now destroyed the lives of over 20 million children and shattered their families.”