The US Senate earlier on Thursday voted to confirm Kennedy 52-48, with senator Mitch McConnell the lone Republican joining all 47 Democrats to vote against Kennedy, who had made pledges to protect existing vaccination programs in a bid to secure votes of hesitant politicians.

Robert F Kennedy Jr initially ran for United States president last year before withdrawing from the race and throwing his support behind Donald Trump. Source: AAP / AP / Alex Brandon

Kennedy will now oversee multiple high-profile agencies, including the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention.

In addition to pledging to work to end chronic disease, Kennedy has said he wants to break any ties between employees at the US drugs regulator and industry.

Robert F Kennedy Jr was sworn in as health and human services secretary alongside Donald Trump, supreme court justice Neil Gorsuch, and members of Kennedy’s family. Source: AAP / AP / Alex Brandon

Ultimately, Senate Republicans closed ranks as they have for every Trump cabinet selection so far.

Democrats accused Kennedy over two days of contentious confirmation hearings of being financially vested in the anti-vaccine movement and peddling conspiracy theories to sow doubt about lifesaving medicines, assertions he rejected.