Chairman Bill Cassidy, a Republican, ended the hearing by speaking to his own experience as a physician and his dedication to saving lives.

Cassidy is a key vote in Kennedy's nomination and has openly expressed reservations about his stance on vaccines. The senator said Thursday his responsibility was to learn if Kennedy can "be trusted to support the best public health."

“You may be hearing from me over the weekend,” Cassidy told Kennedy.

Independent Sen. Bernie Sanders, the ranking member of the committee, got another opportunity to question Kennedy as the hearing neared its end.

But the exchange turned contentious. Kennedy, at one point, referred to the senator simply as "Bernie," and the two yelled about political contributions to the pharmaceutical industry. Chairman Bill Cassidy began banging his gavel on the table in a call to order.

Sen. Bernie Sanders accused Kennedy of praising Andrew Wakefield, the primary author of a now-debunked paper from the U.K. in 1998, which allegedly found that MMR vaccines cause autism.

The paper has since been discredited by health experts and retracted from the journal in which it was published.

In February 2004, The Sunday Times published an investigation, accusing Wakefield of a conflict of interest.

It alleged some of the parents of the children in the paper were suing vaccine manufacturers prior to its publication and Wakefield had received funding to try to find a link between the MMR vaccine and autism, which was not disclosed in the Lancet article. This led to 10 of the 13 authors withdrawing their support.

In 2010, Wakefield lost his medical license after the paper was discredited and an investigation found he had acted " dishonestly and irresponsibly" in conducting his research. More than a dozen high-quality studies have since found no evidence of a link between childhood vaccines and autism.

Republican Sen. Susan Collins of Maine is one key Republican vote to watch throughout Kennedy's nomination.

On Wednesday, she said it was "premature" to decide on Kennedy before the end of the hearings.

During her allotted time for questioning on Thursday, Collins asked Kennedy about his view on certain vaccines and herd immunity, as well as on Lyme disease -- a personal issue for both Collins and Kennedy.

Kennedy assured her he believed the polio vaccine was safe and he would not reduce its availability if confirmed. He also said there's "nobody who will fight harder for a treatment for Lyme disease," which Collins said she appreciated.