The administration of President Joe Biden is buying 500 million doses of the Pfizer-BioNTech Covid-19 vaccine to distribute among other countries, US media reported Wednesday citing people familiar with the matter.

Biden will make the formal announcement at the G-7 meeting in Britain this week, the Washington Post and New York Times said.

The move comes as the United States faces pressure to do more about the global vaccine shortage, with rich countries having bought up the lion's share of early supplies.

The United States itself has fully vaccinated more than half its entire population, and the infection rate has plummeted.

Biden hinted at the announcement before boarding Air Force One bound for Britain to meet with leaders with the Group of 7 nations.

Asked if he had a vaccine strategy for the world, he said: "I have one and I'll be announcing it."

The Times said Biden would appear with Pfizer CEO Albert Bourla to make the announcement.

The deal would see the US paying the "not for profit" price for the doses, with the first 200 million to ship this year and the remaining 300 million the next year.