"Your past of undermining confidence in vaccines with unfounded or misleading arguments concerns me," Republican Senator Bill Cassidy, a physician from Louisiana, told Kennedy on Thursday.Â
"I have constituents who partly credit you for their decision to not vaccinate their child."
"You've cast doubt on some of these vaccines... but the data, and I could quote some of it, the data has been there for a long time."
Kennedy on Wednesday squared off against Democrats on the Senate Finance Committee over his past comments that spread misinformation on vaccines and his shifting stance on abortion rights.
They brought up comments Kennedy has made over decades, including that no vaccine was safe and effective, and quoted other Kennedy remarks made without evidence, including that COVID-19 was targeted to attack Caucasians and Black people, and that it was "highly likely" that Lyme disease was a military bioweapon.
Kennedy, who founded the anti-vaccine group Children's Health Defense, argued during both hearings that he was not against vaccines. On Thursday he said, "I never have said that definitively Lyme disease was created at a biolab."
"News reports and many in the hearing yesterday have claimed that I'm anti-vaccine and anti-industry. Well, I'm neither," Kennedy said, repeating that his children are vaccinated.
He spoke more confidently on Thursday under both Democrat and Republican questioning on detailed health topics ranging from the support for the childhood vaccination schedule and development of the bird flu vaccine.
If confirmed, Kennedy would run the US Department of Health and Human Services, which oversees more than $US3 trillion ($A4.8 trillion) in healthcare spending, including at the Food and Drug Administration and the agency in charge of the Medicare and Medicaid health insurance programs covering nearly half of all Americans.
On Wednesday, Kennedy said he would address rapidly increasing rates of chronic disease and follow Trump's direction on abortion. He also said fewer processed foods should be available in school lunches or for purchase with food stamps, though both of those programs fall under the purview of the US Department of Agriculture.
The Republican-controlled Senate has not rejected any of Trump's nominees so far.
