Kennedy, 69, faces little chance of success, but his campaign could help him to advance claims that childhood immunisations pose health risks – a theory that has been repeatedly discredited by multiple scientific reviews.

Kennedy has been banned from YouTube and Instagram for spreading misinformation about vaccines and the Covid-19 pandemic.

He is the nephew of former President John F Kennedy, who was assassinated in 1963, and the son of former US Senator Robert F Kennedy, who was assassinated in 1968 during his own presidential bid.

Kennedy is likely to highlight these links when he makes his announcement in Boston, the city where his uncles – also including the late US Senator Edward Kennedy – launched their political careers.

His anti-vaccine activism has earned him allies on the right. In 2017, Republican then-president Donald Trump tapped him to oversee a vaccine review panel, drawing criticism from scientists who said it could legitimise unfounded skepticism.

During the Covid-19 pandemic, Kennedy criticised social-distancing requirements and vaccine mandates. At a January 2022 rally in Washington he suggested that Americans had fewer freedoms during the pandemic than Jews living in Nazi Germany. He later apologised for his remarks.

Kennedy said on Twitter last month that he was considering a presidential run to “end the corrupt merger between state and corporate power.”

Self-help guru Marianne Williamson has also said she will challenge Biden for the Democratic nomination.

Biden, 80, said last Friday that he will run for re-election and will make a formal announcement “relatively soon.”