Geneva, Switzerland – The United States will join a UN-led effort to share Covid-19 vaccines fairly between richer and poorer countries, US President Joe Biden's medical advisor Anthony Fauci announced.

Biden would issue a directive on joining the so-called Covax initiative on Thursday, Fauci told an online meeting of the World Health Organization (WHO) executive board.

He said the directive would also signal the plan to join a WHO-led program to speed up the development of Covid-19 vaccines, medications, and diagnostic tools.

Fauci, a top US government disease expert, also reiterated Biden's decision to halt his country's withdrawal from the WHO that had been set in motion by Biden's predecessor Donald Trump.

"I join my fellow representatives in thanking the WHO for its role in leading the global health response to this pandemic," Fauci said, announcing that his administration would resume close cooperation with the Geneva-based UN health agency.

Fauci's comments stood in stark contrast to Trump's allegations that the WHO was to blame for the pandemic because it had helped China cover up the Covid-19 outbreak that was detected in Wuhan in late 2019.

However, Fauci made clear that US stance on a thorough WHO probe into the origins of the outbreak in China has not changed under the new administration.

"The international investigation must be robust and clear," Fauci said, referring to the current WHO-led mission of international experts who are visiting China.