Biden made the announcement at a COVID-19 meeting of world and business leaders and aid groups alongside the U.N. General Assembly. Speaking to the group over video conferencing, Biden said, "We're not going to solve this crisis with half measures or middle of the road ambitions — we need to go big."
The purchase of another 500 million shots brings the total U.S. vaccination guarantee to more than 1.1 billion through 2022. That is more than donations from the rest of the world combined.
However, the latest U.S. donation is only a small part of what will be necessary to meet a goal of vaccinating 70 percent of the world's population by next September.
Biden added that the U.S. would also increase the amount of money given to groups and nations that are administering the shots. He also urged other wealthy nations to donate, rather than sell, the shots to poorer nations. And the European Union said the group would donate another 500 million vaccines, a small increase from its earlier plans.
Some have criticized the plans for being too little. Many people in poor nations have not received their first shot while the U.S. is considering additional booster shots to millions of Americans.
About 6 billion COVID-19 vaccines have been administered worldwide to 43 percent of the world's population in the past year. But many poor nations are struggling to vaccinate even those with the most risk of infection. Some have yet to vaccinate more than 2 percent of their population.
Colombian President Iván Duque said Tuesday at the United Nations, "The existing gaps between nations with regard to the vaccination process are unheard of."
The World Health Organization (WHO) says only 15 percent of promised donations of vaccines from rich countries have been delivered. The health agency has said it wants countries to meet the sharing goals "immediately." The WHO especially wants to make the shots available for programs that benefit poor countries and Africa.
COVAX, the U.N.- supported program to ship vaccines to all countries, has struggled to produce and supply vaccines. The WHO has appealed to wealthy countries to delay booster shots so vaccines can be made available to developing countries. As of Tuesday, COVAX had shipped more than 296 million vaccines to 141 countries.
To deal with the supply problem, Biden said the U.S. would work with drug companies and other nations to produce vaccines in their own country.
I'm Jill Robbins.