The president cited no evidence for his claims.

Research has found no evidence of increased rates of autism among those who are vaccinated compared to those who are not. Vaccines also undergo intensive safety testing. Research shows that genetics play a role in autism diagnoses. The NIH says some possible risk factors for autism include prenatal exposure to pesticides or air pollution, extreme prematurity or low birth weight, certain maternal health conditions, or parents conceiving at an older age.

HHS Secretary Robert F. Kennedy, Jr., said next month, the federal government’s Advanced Research Projects Agency for Health is “preparing a major new initiative focused on foundational causes and biology of autism.”

“We will examine every biologically plausible hypothesis and leave no legitimate, scientific question unexplored,” Kennedy said. “Mr. President, you have told us you want answers, so do I. We have just over two years to finish the work and I know you’re impatient. And we are moving with an urgency that that deadline demands. We will bring you actions and findings as soon as they are read.”

Mr. Trump promised “nothing bad can happen” from the research his administration is doing on autism.