Adams, who served as surgeon general during the first Trump administration, said Kennedy's assertions about the efficacy of mRNA vaccines are "simply not true."

Moderna Inc. shares are selling off Wednesday, after the Trump administration took aim at the science behind the biotechnology company’s vaccines and said it would cancel some contracts and stop funding mRNA drug development.

Notably, RFK Jr. further justified the HHS’s cutting of mRNA vaccine funding by touting other vaccine technologies. “Let me be absolutely clear: HHS supports safe, effective vaccines for every American who wants them. That’s why we’re moving beyond the limitations of mRNA and investing in better solutions,” he said.