The Covax programme, bolstered by the new US presidency, aims to secure enough Covid-19 vaccines this year for the most vulnerable 20% in every country, rich or poor.
Top US government scientist Anthony Fauci told the World Health Organization (WHO) that the United States intends to join Covax, the globally-pooled coronavirus vaccine procurement and equitable distribution effort.
The move should give the facility a much-needed powerful impetus - amid fears that rich countries are undermining the project by cutting their own direct deals with manufacturers.
Since December, dozens of the world's wealthiest countries have begun vaccination campaigns in a bid to halt the coronavirus pandemic.