In language likely to confuse many Americans, the  Centers for Disease Control and Prevention now states that vaccines do not cause autism even as it says the claim is not based on evidence.

The website goes on to say its assurance about vaccines remains on the site only because of a promise made by Health Secretary Robert F. Kennedy, Jr., a vaccine skeptic, during his confirmation hearing.

The CDC autism page was updated on Wednesday to state, “The claim ‘vaccines do not cause autism’ is not an evidence-based claim because studies have not ruled out the possibility that infant vaccines cause autism.”

The site also states, “There are still no studies that support the claim that any of the 20 doses of the seven infant vaccines recommended for American children before the first year of life do not cause autism.”

A bold headline near the top of the page, however, retains earlier language saying: “Vaccines do not cause Autism.” An asterisk leads to a footnote saying the header “has not been removed due to an agreement with the chair of the U.S. Senate Health, Education, Labor and Pensions Committee.”

The chairman of that committee, Senator Bill Cassidy, solicited the pledge from Mr. Kennedy before casting one of the deciding votes to confirm the health secretary in his post.

Mr. Cassidy, a board-certified doctor with three decades of experience, responded to the website change on Thursday with a pro-vaccine message on X that did not directly address Mr. Kennedy’s action or his pledge.

“What parents need to hear right now is vaccines for measles, polio, hepatitis B and other childhood diseases are safe and effective and will not cause autism. Any statement to the contrary is wrong, irresponsible, and actively makes Americans sicker,” he wrote.

“It’s deeply troubling that, according to HHS officials, they appeared to have canceled hundreds of millions in research on autism genetics,” Mr. Cassidy’s post continued. “Redirecting attention to factors we definitely know DO NOT cause autism denies families the answers they deserve.”

A spokesman for the senator referred questions from The New York Sun to Mr. Cassidy’s X post.

The Autism Science Foundation says the new wording on the CDC’s autism page distorts science and rejects decades of evidence on vaccine safety.

“The CDC’s previous science and evidence-based website has been replaced with misinformation and now actually contradicts the best available science,” the foundation said in a statement on Thursday.

Mr. Kennedy has a long history of being a vaccine skeptic. Earlier this year he promised that he would uncover the cause of the autism epidemic in America within just a few months. He later backed away from that deadline.

In September he suggested that Tylenol use during pregnancy could potentially be linked to autism and, in an October cabinet meeting, claimed that circumcised boys are twice as likely as others to develop autism. He suggested the missing link may be Tylenol administered to newly circumcised boys.