Sen. Bill Cassidy, a Louisiana Republican and chairman of the Senate Health, Education, Labor and Pensions Committee, criticized President Donald Trump’s vaccine proposals Sunday during an appearance on CBS’ “Face the Nation.” Cassidy, who is also a physician, demanded that Trump explain the basis for his plan to split some childhood vaccines into five separate doses.

Trump said Friday that he would demand that drug companies divide certain childhood vaccines into five doses, claiming the change could produce “a massive reduction in autism.” Trump did not specify which vaccines would be affected or provide scientific evidence for the claim.

Cassidy said he did not know which vaccines Trump was referring to or where the proposal originated. He called for what he described as “radical honesty” and said vaccines have been proven safe. Cassidy also warned that discouraging immunization could result in more people becoming sick, hospitalized or dying from diseases such as measles.

Cassidy has become increasingly vocal in opposing parts of the Trump administration’s vaccine agenda. At a Senate hearing earlier this month, he challenged Surgeon General nominee Dr. Nicole Saphier over vaccine safety and criticized changes to the childhood immunization schedule. Cassidy has also questioned FDA commissioner nominee Dr. Heidi Overton’s role in the administration’s vaccine policy.

On Sunday, Cassidy said he wants Overton to reject Trump's previous characterization of the measles vaccine as lethal. He called that characterization “absurd” and argued that federal health officials should clearly communicate that the measles vaccine is safe and effective.

Cassidy pointed to the ongoing measles outbreak as part of his argument. Reuters reported this week that Pennsylvania had more than 700 confirmed measles cases and four associated deaths, while the state requested federal assistance amid a dispute with the CDC over how the deaths should be classified.

The disagreement places Cassidy, a Republican who chairs the Senate committee responsible for overseeing federal health agencies, at odds with important elements of Trump's health agenda. Cassidy has argued that public health policy should be based on evidence and that uncertainty surrounding the administration's vaccine messaging could further reduce public confidence in childhood immunization. A recent Reuters/Ipsos poll found that the share of Americans who said measles vaccines are safe had declined from 84% in 2020 to 76% in September 2026.