WASHINGTON — The United States has purchased and will donate 500 million doses of Pfizer"s COVID-19 vaccine worldwide as it seeks to be a key player in getting other nations vaccinated. President Joe Biden will announce the news at the G7 summit in Cornwall, England, this week. Around 200 million doses will go out in 2021 and 300 million will be distributed in the first half of 2022. Biden"s top coronavirus adviser, Jeff Zients, has been working on the deal for the last month, a person familiar said. All doses will go through COVAX, the international vaccine initiative, and will go to 92 low- and lower-income countries, in addition to the African Union. White House national security adviser Jake Sullivan told reporters aboard Air Force One on Wednesday that in addition to the Pfizer purchase, Biden is also expected to take part in a combined announcement with the G7 on a comprehensive plan to end the pandemic. It will include a segment on vaccines. Sullivan argued that having the US play a leading role in global Covid-19 vaccine distribution is part of what Americans do in times of need and would be advantageous to prevent the future spread of the disease in the US. "He does want to show rallying the rest of the world"s democracies — the democracies are the countries that can best deliver solutions for people everywhere. That goes for COVID-19, that goes for climate change, it goes for economic recovery and it goes for the basic human rights and human dignity of all people," Sullivan said. Biden had previously committed to sharing 80 million vaccine doses with other countries. That share included Pfizer doses as well. Last week, the Biden administration announced its 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. At least 75 percent of those donated vaccines will be shared with the global vaccination program called Covid-19 Vaccines Global Access, or COVAX, and 25 percent 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. The US president has said there will be enough COVID-19 vaccine supply for every American adult by the end of June and has set a goal of having 70 percent of US adults vaccinated by July 4. The US, however, remains on track to fall short of that goal. — CNN