Falmouth, England CNN  — 

President Joe Biden announced Thursday evening that the United States plans to donate 500 million Pfizer Covid-19 vaccine doses globally as part of his efforts to reassert US leadership on the world stage.

“America knows first-hand the tragedy of this pandemic. We’ve had more people die in the United States than anywhere in the world, nearly 600,000 of our fellow Americans,” Biden said in remarks after meeting with British Prime Minister Boris Johnson.

He added, “We know the tragedy. We also know the path to recovery.”

The move will also serve to counter efforts by Russia and China to use their own state-funded vaccines to expand their global influence.

“American workers will now produce vaccines that save lives of people in Africa, Asia, Latin America and the Caribbean – people they will never meet and have never met. Places they’ve never visited and probably won’t have an opportunity to. But lives saved all the same, thanks to American leadership, American workers, hard work and values,” Biden said on Thursday.

White House officials brokered a deal with Pfizer to secure half-a-billion doses of its coronavirus vaccine over the course of just four weeks as they raced to secure a deal ahead of the G7 summit, a senior White House official told CNN. Over those four weeks, White House officials – led by Jeffrey Zients, the White House’s coronavirus coordinator whom Biden also tapped to lead the international vaccine distribution effort – engaged in near-daily negotiations with several US-based vaccine manufacturers, ultimately selecting Pfizer because the company “could deliver the fastest.”

Hundreds of millions of doses of Russia’s Sputnik V vaccine, along with China’s Sinovac and Sinopharm shots, have been making their way around the world. Only the Sinopharm vaccine has been accepted into the World Health Organization’s COVAX initiative.

Many countries – including in Latin America, which has traditionally been an area of US influence – have been buying up large numbers of Russian and Chinese vaccines to fill the gaps in their own vaccine rollouts.

The White House has said it has been monitoring and is concerned by efforts by Russia and China to use vaccines to make geopolitical gains.

During remarks announcing the vaccine purchase, Biden underscored that there were no strings attached with accepting the US-bought vaccines.

‘Let me be clear: Just as with the 80 million doses we previously announced, the United States is providing these half-(billion) doses with no strings attached,” Biden said. “Our vaccine donations don’t include pressure for favors or potential concessions. We’re doing this to save lives, to end this pandemic. That’s it. Period.”

Administration officials suggested the move is part of a broader effort for the world’s democracies to lead the way in pandemic recovery.

“This will be clearly the largest purchase and donation of Covid-19 vaccines by a single country, by far, and it’s an unprecedented response,” a senior administration official told reporters Thursday.

“We want to do everything we can to prevent more tragic loss across the globe,” the official said, adding that it is “in our national interest to end this pandemic everywhere.”

“Covid-19 knows no borders, and as long as this virus is in our world, Americans are at risk,” the official said, stressing how the virus also “threatens economic opportunity.”

The move to donate doses is also intended to encourage other US allies to step up.

“We’re also using this announcement today to leverage and mobilize larger commitments from the world’s democracies, from the G7 and partner countries,” a separate senior official said, previewing a “G7 Covid-related multilateral announcement.”

At the G7 summit this weekend, the official said, leaders will announce a “collective effort by the world’s democracies to beat Covid-19 for once and for all.”

The donation comes as Biden has repeatedly said that the world is at an inflection point to show whether democracy can prevail over autocracy.

As for a timeline, officials said the Pfizer doses will begin to ship in August and 200 million doses will be delivered by the end of this year. The remaining 300 million doses will be delivered in the first half of 2022. They will be manufactured in the US, the officials said, “employing thousands of workers” in states like Michigan, Connecticut and Massachusetts. The cost will be around $1.5 billion, which will come from previously allocated funds in the American Rescue Plan relief package passed earlier this year.

Biden had previously committed to sharing 80 million Covid-19 vaccine doses with other countries. Last week, the Biden administration announced a plan to share the first 25 million Covid-19 vaccine doses with the rest of the world and an overall framework of distributing at least 80 million doses by the end of June.

About 75% of those donated vaccines will be shared with the global vaccination program called Covid-19 Vaccines Global Access, or COVAX, and about 25% will be shared directly with countries in need, the White House said.

Biden said last month the US would share an additional 20 million doses of Covid-19 vaccines by the end of June on top of the 60 million doses of the AstraZeneca vaccine the President had already committed to sharing by July 4. The additional 20 million doses will consist of Moderna, Pfizer and Johnson & Johnson vaccines as well as AstraZeneca, which has to be approved by federal regulators before being shipped overseas.

This story has been updated with additional developments.

CNN’s Jeremy Diamond contributed to this report.