Robert F. Kennedy Jr. lashed out at Senator Bernie Sanders, a Vermont independent, sparking a heated exchange between the two at the end of the Senate health committee hearing Thursday.

Mr. Sanders pushed Mr. Kennedy again on his past support for the claims that vaccines caused autism. He also mentioned Mr. Kennedy’s praise for Andrew Wakefield, the British scientist whose research fueled speculation that immunizations and autism were linked. His work has since been debunked.

When Mr. Kennedy offered that he wouldn’t “rest on a single study,” Mr. Sanders sought to introduce into the record 16 studies that concluded vaccines do not cause autism.

Mr. Sanders held up the papers and asked, “Are you happy?”

Mr. Kennedy asked the senator if he included an analysis by the Institute of Medicine, indicating that it would support his position. But that report said the body of evidence favored rejecting a direct link between some vaccines and autism.

As Mr. Kennedy tried to elaborate, Mr. Sanders waved his hand to stop him, saying “don’t have a lot of time.”

Later, Mr. Sanders questioned Mr. Kennedy about his previous remarks calling the coronavirus vaccine one the deadliest vaccines ever made. Early estimates found that Covid vaccines and other mitigation measures saved 800,000 lives in the United States, and that Covid death rates were 14 times higher among unvaccinated people compared to those who received the Covid booster shot.