Both Republicans and Democrats clash with RFK Jr. on vaccines, CDC turmoil

Democratic Sen. Michael Bennet grilled Kennedy on his firing of all 17 members of the CDC's vaccine advisory panel, the Advisory Committee for Immunization Practices, and the panel's upcoming review of childhood vaccine schedule recommendations later this month.

The exchange turned heated as both men raised their voices.

"I'm asking the questions, Mr. Kennedy, on behalf of parents and schools and teachers all over the United States of America who deserve so much better than your leadership," Bennet yelled. "That's what this conversation is about."

"Senator, they deserve the truth, and that's what we're going to give them for the first time in the history of that agency," Kennedy responded.

RFK Jr. doubled down on the false accusation that mRNA COVID-19 vaccines cause serious harm, including death among young people.

This question has been heavily studied in the wake of the rare risk of myocarditis among younger adults.

The data do not support a link between mRNA vaccines and sudden cardiac death among previously healthy young people.

-ABC News' Sony Salzman

Kennedy claimed the COVID-19 pandemic was "politicized" and that Americans were lied to.

He claimed it was untrue that COVID-19 vaccines would prevent transmission and infection.

Studies of the original vaccine found it to be 90% effective against lab-confirmed, symptomatic infection and 100% effective against moderate and severe disease, according to Yale Medicine.

Most Democrats on the Senate Finance Committee -- which has oversight over HHS and is questioning Kennedy today -- put out a statement before Tuesday's hearing calling for RFK Jr's resignation.

"Robert Kennedy has failed to protect the health of the American people and endangers the lives of all Americans, particularly children, people with disabilities, and vulnerable Americans. Robert Kennedy must resign, and if he doesn’t, Trump should fire him before more American families are hurt by his reckless disregard for science and the truth," the group of 12 senators wrote.

Kennedy avoided reporters' questions before the hearing started, as did Republican Sen. Bill Cassidy.

Democratic Sen. Mark Warner who signed the letter, however, stressed his calls for Kennedy's removal.

"Absolutely. Purely based on the fact that he's completely gone against what he pledged to this committee and to my friend Bill Cassidy," he told ABC News.

-ABC News' Jay O'Brien and Allison Pecorin