The US has formally notified the World Health Organization of its withdrawal, despite widespread criticism and an almost complete lack of international support for the move in the midst of a pandemic. Donald Trump announced his intention to withdraw in May, accusing the WHO, without evidence, of withholding information, and of being too close to China. The letter confirming the move was delivered to the UN secretary general, António Guterres, officials confirmed on Tuesday. A WHO official said: “We have received reports that the US has submitted formal notification to the UN secretary general that it is withdrawing from WHO effective 6 July 2021.” Trump’s Democratic challenger for the presidency, Joe Biden, said he would return the US to the WHO before the year-long process of withdrawal was complete. “Americans are safer when America is engaged in strengthening global health,” Biden said on Twitter. “On my first day as President, I will rejoin the @WHO and restore our leadership on the world stage.” Democrats have also questioned the legality of the move without congressional approval. But the administration has already begun looking for other channels to spend the $450m it pays annually in WHO membership dues and voluntary contributions. It is unclear what will happen to US officials who work with the global health body. Jeff Merkley, the top Democrat on the Senate foreign relations subcommittee that oversees multilateral institutions, called the move “a huge win for China and a huge blow to the American people”. “By pulling out of the WHO, President Trump is strengthening Chinese leadership and power, both within the WHO and more broadly within the international community,” Merkley said. “Cutting the United States out of the WHO in the middle of the worst global pandemic in a century makes Americans more vulnerable. By abandoning the efforts to control the virus abroad, we’re ensuring that far more Americans will get sick, either through foreign travelers coming to the US, or through Americans traveling abroad.” Republican members of Congress have also urged Trump to keep the US inside the WHO to support reform. The administration has received almost no support for withdrawal from US allies, with the exception of the Brazilian president, Jair Bolsonaro, who confirmed he had tested positive for coronavirus on Tuesday. The formal withdrawal was confirmed as the number of US coronavirus cases approached 3 million, with 130,000 deaths so far. The White House coordinator on coronavirus response, Deborah Birx, said the administration had been caught by surprise by the spread among younger Americans. “I think none of us really anticipated the amount of community spread that began in our 18-to-35-year-old age group and I think that this is an age group that was so good and so disciplined through March and April, but when they saw people out and about on social media, they all went out and about,” Birx said at a roundtable with foreign ambassadors and senior diplomats organised by the Atlantic Council. Birx left the online meeting before news of the formal withdrawal arrived. None of the foreign diplomats taking part supported the move. “While criticism is welcome … we feel that it is not a good idea to hamper the organization, while in the full thrust and brunt of this pandemic,” the German deputy head of mission, Ricklef Beutin, said.