Robert F. Kennedy Jr., the nation’s health secretary, on Saturday instructed leaders of the nonprofit he founded to take down a web page that mimicked the design of the Centers for Disease Control and Prevention’s site but laid out a case that vaccines cause autism.

The page had been published on a site apparently registered to the nonprofit, the anti-vaccine group Children’s Health Defense. Mr. Kennedy’s action came after The New York Times inquired about the page and after news of it ricocheted across social media.

The page was taken offline Saturday evening.

“Secretary Kennedy has instructed the Office of the General Counsel to send a formal demand to Children’s Health Defense requesting the removal of their website,” the Health and Human Services Department said in a statement.

“At H.H.S. we are dedicated to restoring our agencies to their tradition of upholding gold-standard, evidence-based science,” the statement said.

It was not clear why the anti-vaccine group might have published a page mimicking the C.D.C.’s. The organization did not respond to requests for comment, and Mr. Kennedy has said he severed ties with it when he began his presidential campaign in 2023.

The fake vaccine safety page was practically indistinguishable from the one available on the C.D.C.’s own site. The layout, typefaces and logos were the same, perhaps in violation of federal copyright law.