The US is to distribute half a billion shots of the Pfizer vaccine to nearly 100 poorer countries.
Some 200 million doses will be given out this year and 300 million in 2022.
It comes as US President Joe Biden said before leaving for the G7 summit in Cornwall that he would be announcing a vaccine strategy for the world.
The US will pay for the doses at a “not-for-profit” price, according to the New York Times, which said the plan could be officially announced on Thursday.
The shots will go to 92 lower-income countries and the African Union, but Pfizer and the White House have so far not commented.
America is well advanced in its vaccine rollout but campaigners have called for richer countries to do more to help protect developing nations.
The half a billion jabs will be distributed via the World Health Organization’s (WHO) Covax scheme, which is trying to fix so-called “vaccine apartheid” by working with governments and manufacturers to ensure an equitable distribution of jabs.
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It aims to deliver two billion doses in 2021, and 1.8 billion doses by early 2022.
Only 2% of Africa’s population have received at least one dose of a vaccine, while globally it’s 24%, says the WHO.
In the UK, the figure is about 60%, and around 50% in America.
The urgency is highlighted by a recent 20% increase in COVID cases in Africa compared with the previous fortnight.
In a statement last week, the WHO said the pandemic was trending upwards in 14 countries on the continent – but that vaccine shipments were continuing to slow down.
The Biden administration had already pledged to share 80 million vaccine doses globally by the end of June, with the first shipments due in the next few weeks.
Along with jabs for its own population, the New York Times said the new pledge would take the Pfizer-Biontech shots bought by the US to 800 million.