Robert F. Kennedy Jr.'s views on vaccines are dangerous, his cousin and outgoing U.S. ambassador to Australia Caroline Kennedy said on Monday, days after Donald Trump picked him to head the United States' top health agency.

Caroline Kennedy said RFK Jr.'s views on vaccines are "dangerous" and at odds with that of most Americans, including the Kennedy clan.

"I grew up with him, so I've known all this for a long time. Others are just getting to know him," she said, drawing laughter from the crowd at the National Press Club in Canberra.

"I would say that our family is united in terms of our support for the public health sector and infrastructure and has greatest admiration for the medical profession in our country, and Bobby Kennedy has got a different set of views."

RFK Jr., the son and nephew of two titans of Democratic politics, wants to tackle what he calls the "chronic disease epidemic" of conditions including obesity, diabetes and autism.

But critics point to his history of making false medical claims, including statements that vaccines are linked to autism.

Kennedy disputes the anti-vaccine tag, saying he instead wants more rigorous testing of vaccines. However, he chaired the Children's Health Defense, a nonprofit organisation that focuses on anti-vaccine messaging.

Kennedy ran for president in this year's election as an independent before dropping out in August and endorsing Trump in exchange for a role in the Republican's administration.

The Kennedy name is powerful currency in Democratic politics. Caroline Kennedy is the daughter of the late U.S. President John F. Kennedy.

In one of her last speeches as ambassador, Kennedy told the Canberra audience Australia and the Indo-Pacific would remain important to the U.S. regardless of who was president.

"The United States has made commitments over many decades and those are not going to change and our national interest is not going to change," she said.

She also said Americans would elect a female President in her lifetime, but demurred when asked if it would be her.