Updated September 22, 2021 at 5:00 PM ET

President Biden called on rich nations and philanthropists to do more to end the pandemic, saying the United States will buy 500 million more doses of the Pfizer-BioNTech vaccine to donate to countries around the world for delivery by next September.

The White House said the goal is to vaccinate 70% of the world's population for COVID-19 by this time next year.

"We're not going to solve this crisis with half-measures or middle-of-the-road ambitions. We need to go big," Biden said at a virtual summit.

Biden's goal fell short of what global health advocates have been pushing for. Those tensions came out during the summit.

During his remarks, which were not open to the press, U.N. Secretary-General António Guterres reiterated a call for a more ambitious goal: vaccinating 40% of people in all countries by the end of this year and 70% in the first half of 2022.

Guterres was critical of wealthy nations scooping up vaccine contracts for their own populations while middle-income countries compete for doses in a seller's market and poor countries are left to wait for donations.

"High-income countries have administered 61 times more doses per inhabitant than low-income countries," Guterres said, noting earlier pledges by Group of Seven leaders have not yet fully materialized. "Just 3% of Africans have been vaccinated."

It's a big donation, but more doses are needed

Biden's pledge will bring the total promised U.S. vaccine donations to more than 1.1 billion. So far, the U.S. has shipped almost 160 million doses to 100 countries around the world, a number that exceeds all other donations combined, a U.S. official told reporters ahead of the summit.

But to reach the 70% goal, about 5 billion more doses need to be donated to low- and middle-income countries, said Carolyn Reynolds, co-founder of the Pandemic Action Network. That means the U.S. pledges account for about one-fifth of the global need.

"The challenge now is timing and delivery," Reynolds said. There should be enough supply by early next year, but then distribution will be the next challenge to overcome. More work is needed to get shots in arms much faster, Reynolds said.

Reynolds, who delivered a video statement at the summit, described the virtual gathering as a "critical reset" of the global vaccination drive, which has come up short on earlier ambitions. But she hopes the 70% target will be hit before Biden's deadline.

Booster shots criticized

The United States and other wealthy countries have poured resources into plans to offer booster shots to fully vaccinated people, even as vast swaths of the world have yet to receive a single shot, prompting pleas from the World Health Organization and others to do more to slow the spread globally.

Biden defended the U.S. response, saying his first responsibility was to make sure Americans were protected and arguing that the U.S. donations have been generous. "For every one shot we've administered to date in America, we have now committed to do three shots to the rest of the world," Biden said.

The new tranche of Pfizer doses will be manufactured in U.S. plants and will be bought at a "not-for-profit" price, officials said. Most U.S. vaccine shipments — 800 million doses — will ship between January and September 2022.

More than vaccines are needed

Biden convened the summit to coincide with the U.N. General Assembly in New York, a meeting that has been scaled back because of the risks of spreading COVID-19. During a portion of the summit open to the press, Biden sat on a stage set built to look like an office as eight world leaders looked back at him from a giant screen.

The White House did not provide a list of speakers and participants in the summit, which was closed to the press except for speeches from Biden and Vice President Harris. But advocates invited to the event provided some details of what was happening on social media.

The White House set specific targets for vaccines as well as donations of oxygen, tests, therapeutics and protective gear to parts of the world that need it — and will work on a health security financing mechanism so that the world is more prepared for future pandemics.

The Biden administration is also investing in vaccine manufacturing plans in Africa and India that together will be able to produce 2 billion doses by 2022, the White House said.

Biden called on other countries to donate — not sell — doses and said there would be follow-up sessions later this year and early next year to check on progress.

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