Sen. Maggie Hassan, a New Hampshire Democrat, confronted Robert F. Kennedy Jr. about his insistence on falsely linking vaccines to autism, saying the issue was a deeply personal one for her.

On Thursday at Kennedy’s second confirmation hearing for his nomination for health secretary, Hassan took issue with her Republican colleagues’ suggestion that the tough questioning that Kennedy faced was driven by partisanship.

Hassan choked up as she talked about her 36-year-old son, who has severe cerebral palsy. “A day does not go by when I don’t think about: ‘What did I do when I was pregnant with him that might have caused the hydrocephalus that has so impacted his life?’” she said. “So please do not suggest that anybody in this body of either political party doesn’t want to know what the cause of autism is.”

Kennedy has long promoted false claims about the safety of vaccines, including that they cause autism — a long-debunked theory. During his two confirmation hearings before Senate committees this week, he repeatedly refused to say if he agreed that vaccines do not cause autism.

Hassan has talked publicly about her son and his disability in connection with health care issues in the past. On Thursday, she brought up a now-disproven study that claimed to show a link between vaccines and autism, saying that when the study was published, “it rocked my world.” But that research, which was conducted with a minuscule sample size, has been debunked over and over, she said, and the journal later retracted the study “because sometimes, science is wrong.”

“When you continue to sow doubt about settled science, it makes it impossible for us to move forward,” Hassan told Kennedy. “So that’s what the problem is here, is the relitigating and the rehashing and the continuing to sow doubt so we can’t move forward. And it freezes us in place.”

Rarely has Kennedy, a leading anti-vaccine activist, been challenged on his views in such a high-profile setting. He sought to distance himself from his past comments on vaccines in his hearings, though Democratic senators — and at least one Republican, Sen. Bill Cassidy, a physician — appeared skeptical of Kennedy’s apparent about-face.