World Health Organization (WHO) chief Tedros Adhanom Ghebreyesus on Wednesday hailed the United States' support for a global waiver on patent protections for Covid-19 vaccines, describing it as a "historic decision".

The WHO chief wrote on Twitter that the move was a step towards vaccine equity, "prioritizing the well-being of all people everywhere at a critical time".

"Now let's all move together swiftly, in solidarity, building on the ingenuity and commitment of scientists who produced life-saving Covid-19 vaccines," he added.

Tedros has for months pleaded for such a patent waiver -- an idea backed by India and South Africa -- arguing this would help to ramp up production and make Covid-19 vaccines much more accessible for poorer nations.

"If not now, when?" has become a frequent refrain from the WHO chief, who has lashed out repeatedly against perceived vaccine-hoarding by richer nations.

Tedros clashed repeatedly with former US president Donald Trump, who began withdrawing his country from the WHO before President Joe Biden immediately rescinded the move upon taking office in January.

A later tweet from the WHO chief on Tuesday appeared to confirm that things had got off to a better start with Biden.

"This is a monumental moment in the fight against #COVID19," he said of US support for the patent waiver, describing Biden's commitment as "a powerful example of leadership to address global health challenges".