The donation will complete Washington’s initial pledge of 80 million doses from its own vaccine supply, made ahead of a vow to buy 500 million doses of Pfizer’s vaccine for low- and middle-income nations.

41 million of the 55 million doses (75%) are being distributed through the Covax programme, with the remaining 14 million (25%) shared with recipients the US deems priorities.

The vaccines being shared with Covax include 14 million for Latin America and the Caribbean, approximately 16 million to Asia, and 10 million for Africa in coordination with the African Union.

The first tranche included the Johnson & Johnson, Moderna and Pfizer-BioNTech vaccines, but it was not immediately clear what the second tranche would comprise.

A vaccine created by AstraZeneca has yet to earn US authorisation but is in use elsewhere.

While wealthy countries are ramping up vaccinations and returning to normal, Covid cases are surging elsewhere, including in South America and Africa.

Less than 1% of Covid vaccine doses globally have been administered to people in low-income countries.

“The Biden administration’s plan for sharing more Covid-19 vaccine doses globally will help end the pandemic faster and save lives,” said Tom Hart, acting CEO of The One campaign to eradicate poverty and preventable disease.