Joe Biden’s administration will join global efforts to make Covid-19 vaccines and drugs available around the world, reversing the position of his predecessor Donald Trump and ushering in a new era in health diplomacy.

Anthony Fauci, head of the National Institutes of Allergy and Infectious Diseases, said on Thursday that the US would sign up to the World Health Organization’s Covax programme to “advance multilateral efforts” to halt the spread of coronavirus.

Speaking to the WHO’s executive board a day after Mr Biden’s inauguration as president, Dr Fauci said he was “honoured” to say the US would remain a member of the WHO.

“The US stands ready to work in partnership and solidarity to support the international Covid-19 response, mitigate its impact on the world, strengthen our institutions, advance epidemic preparedness for the future and improve the health and wellbeing of all people throughout the world,” Dr Fauci said.

Mr Trump, who left the White House on Wednesday after one term as president, had said the US would quit the Geneva-based organisation, which he accused of pandering to China and not acting quickly enough to warn the world about the pandemic.

The move is part of Mr Biden’s early attempt to undo much of Mr Trump’s legacy as president and return the US to a more internationalist outlook, which also included a day-one move to rejoin the Paris climate accord.

The new president promised in his inaugural address on Wednesday that his country would lead the world “not merely by the example of our power, but by the power of our example”.

Mr Biden will speak to Justin Trudeau, Canada’s prime minister, on Friday, before prioritising calls with other allies, according to Jen Psaki, the White House press secretary.

Of the WHO, Dr Fauci said the US would resume “regular engagement” with the body and that it intended to fulfil financial obligations. He also endorsed the WHO mission to China to probe how the virus originated.

“It is imperative that we learn and build on important lessons about how future pandemic events can be averted,” said Dr Fauci. “The international investigation [into the pandemic’s origins] must be robust and clear, and we look forward to evaluating it.”

Tedros Adhanom Ghebreyesus, WHO director-general, welcomed the US re-engagement. “This is a good day for the WHO and a good day for global health . . . We must work together as one family,” he said.

Jeremy Farrar, director of medical charity the Wellcome Trust, praised the US move to join Covax, saying strong international collaboration would be “key to ending this pandemic as quickly as possible and improving the lives of millions of people worldwide”.

The Covax facility, which is also convened by the Gavi alliance of vaccine partners and the Coalition for Epidemic Preparedness Innovations, has struggled to mobilise the support needed to fulfil its mission of making 2bn vaccine doses available equitably across the world.

That difficulty, coupled with vaccine nationalism that has led richer countries to buy up supplies, has forced some lower-income countries to negotiate procurement deals independently, leaving them potentially exposed to months without urgently needed vaccinations.

Suerie Moon, co-director of the global health centre at Geneva’s Graduate Institute, said the US had “suffered severe reputational damage under Trump” but that it remained a global leader in health.

“[US participation] will give Covax a big shot in the arm with money [and] access to existing vaccine supply,” she said. “And through use of government authority to compel production and transfer technology, it can make huge strides towards increasing vaccine supply for the world.”

Additional reporting by Kiran Stacey in Washington