MORE: What we know about the safety, efficacy of mRNA vaccines amid recent scrutiny. Public health experts told ABC News the position Kennedy and those in his circle have taken on

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."

Robert F. Kennedy Jr. has announced that his department will end funding for a series of mRNA-based vaccines aimed at preventing major respiratory illnesses.