On his first day as U.S. President, Joe Biden has stopped his country's withdrawal from the World Health Organization (WHO).

Former President Donald Trump had initiated the process of the U.S. withdrawal from the organization in July 2020 and he also froze all its funding.

Thursday's decision was celebrated by the WHO during its executive board meeting.

"This is a good day for WHO and a good day for global health," said the organization's director-general, Tedros Adhanom Ghebreyesus. "Thank you President Biden for honouring your pledge to maintain the membership of the United States in WHO," he added.

Anthony Fauci, the U.S.'s top infectious diseases expert, officially made the announcement in front of the WHO executive board on Thursday morning, as the new head of the American delegation.

Fauci confirmed the U.S. will stop reducing the number of American staff working at the WHO and, most importantly, he said the U.S. will fulfill all its financial obligations with the organization.

The U.S. is the largest single contributor to the WHO – in 2019 it contributed $400 million – and so, at this point of the pandemic, that funding will be crucial for the WHO, especially when it comes to helping lower-income countries.

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Fauci told the WHO executive board: "As a WHO member state, the United States will work constructively with partners to strengthen and, importantly, to reform the WHO."

He also announced the U.S. will join COVAX, the global initiative to develop and deploy the COVID-19 vaccines.

"I am also pleased to announce today that the United States plans to work multilaterally to respond and recover from the COVID-19 pandemic. President Biden will issue a directive later today, which will include the intent of the United States to join COVAX," he said.

Thursday marked a year since the first case of COVID-19 was reported in the U.S..  By joining the COVAX initiative Joe Biden is signaling that he is serious in prioritizing the fight against the pandemic, at home and abroad.

"Since the WHO's founding in 1948, the United States has played a vital role in global health and the American people have made enormous contributions to the health of the world's people," Adhanom Ghebreyesus said. "We look forward to continuing this partnership, as I know all member states do."

He added: "WHO is a family of nations and we are all glad that the United States is staying in the family."