A Centers for Disease Control and Prevention website that previously said that vaccines do not cause autism walked back that statement, contradicting the agency’s previous efforts to fight misinformation about a connection between the two.

The agency’s webpage on vaccines and autism, updated on Wednesday, now repeats the skepticism that Health Secretary Robert F. Kennedy Jr. has voiced about the safety of vaccines, though dozens of scientific studies have failed to find evidence of a link.

A previous version of the webpage said that studies had shown “no link between receiving vaccines and developing autism spectrum disorder.” It cited a 2012 National Academy of Medicine review of scientific papers and a C.D.C. study from 2013.

On Thursday, the live version of the page stated: “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 updated text also claimed that the health authorities have “ignored” studies supporting a link and said that the Department of Health and Human Services was conducting a “comprehensive assessment” of the causes of autism.

Studies over the past three decades consistently have not found any connection between vaccines and autism, including one from 2019 in Denmark that examined the country’s entire child population over a decade.

The phrase “Vaccines do not cause autism” still appeared on the new C.D.C. page. A footnote explained that the language had not been removed because of an agreement with Senator Bill Cassidy, Republican of Louisiana, that it remain on the C.D.C. website. Senator Cassidy is a medical doctor and is the chairman of the Senate’s Health, Education, Labor and Pensions Committee. At least one other C.D.C. page continued to say there was no link, as did a page on the website for the Food and Drug Administration, which Mr. Kennedy also oversees.

Senator Cassidy’s office did not immediately respond to a request for comment.

Andrew Nixon, the communications director for the Health and Human Services agency, defended the change and reiterated that it had begun “a comprehensive assessment of the causes of autism.”

The new webpage pleased anti-vaccine activists. “Finally, the CDC is beginning to acknowledge the truth about this condition that affects millions,” said Children’s Health Defense, an anti-vaccine organization founded by Mr. Kennedy, on social media on Wednesday.

Doctors, epidemiologists and public health experts condemned it. “This revision represents political pressure overriding scientific consensus,” Dr. Jake Scott, an infectious disease physician at Stanford University, said on social media on Thursday, calling the change “a dangerous precedent for evidence-based medicine.”

In a statement, the Autism Science Foundation said it was “appalled” by the new webpage, saying the page “is now filled with anti-vaccine rhetoric and outright lies about vaccines and autism.” “The facts don’t change because the administration does,” Alison Singer, the foundation’s president, said in a statement.

The C.D.C. also took down a page that advised pregnant women on the benefits of Covid-19 vaccination. “This page’s content is currently being updated to align with” recent recommendations from the Advisory Committee for Immunization Practices, the page now says. It is unclear when the revised content might appear.