Donald Trump spokeswoman Elizabeth Emken, a former executive with the leading advocacy group Autism Speaks, was put in a difficult position Monday when asked about the frontrunner’s earlier statements linking vaccines and autism.

Asked on CNN about Trump suggesting a scientific link exists between childhood vaccines and autism during a fall 2015 presidential debate, Emken sidestepped a direct rebuke of Trump’s claims.

“The position of Autism Speaks has been for quite awhile that we need to find out what’s happening,” she replied. “We know there’s a genetic component and there’s an environmental trigger and until we get to the bottom of what’s happening, no one knows what causes autism. Anyone that tells you what does or what doesn’t cause autism is simply not basing that on facts.”

“We don’t know, we need to keep looking,” Emken continued, saying she hadn’t discussed the issue with the GOP frontrunner. “But the bottom line is, look, vaccines are the most successful health program in the history of the world, so I don’t believe that’s at all what he was saying.”

As recently as September 2015, Trump regularly tweeted about vaccines and autism, attacking what he saw as a correlation between the “massive dose” in the combined mumps, measles and rubella vaccine and rates of autistic children.

I’m not against vaccinations for your children, I’m against them in 1 massive dose.Spread them out over a period of time & autism will drop! — Donald J. Trump (@realDonaldTrump) September 4, 2014

Emken joined Autism Speaks as a government relations staffer in 2007 and previously worked for Cure Autism Now.

While Autism Speaks definitively said vaccines do not cause autism in a March 2015 statement, the group previously funded research into the now widely-discredited claim. The stance caused a senior executive to resign her post in 2009.