The White House said that the Biden administration will purchase 500 million more doses of Pfizer’s COVID-19 vaccine to donate to low- and middle-income countries, bringing the total number of shots committed by the U.S. for the global supply to 1.1 billion.

President Biden announced the news during a virtual COVID summit on the sidelines of the United Nations General Assembly on Wednesday. The doses of Pfizer’s vaccine will begin shipping out to countries in January, and Mr. Biden said the 500 million doses will all be shipped by September 2022. The U.S. has so far committed to giving more than 600 million vaccine doses to other nations. Nearly 160 million of these vaccine doses have been shipped abroad thus far.

Mr. Biden has stressed that defeating the COVID-19 pandemic requires a global response, and he called on fellow world leaders at the start of Wednesday’s summit to do more to enhance equitable access to vaccines, expand availability of tests and therapeutics, and take steps to prepare for the next pandemic.