"Today, we will hit a major milestone in our global effort: 400 million vaccine doses shipped to 112 countries ... for free, no strings attached," White House COVID-19 Coordinator Jeff Zients told reporters at a briefing.
The latest batch includes 3.2 million doses of the Pfizer Inc and BioNTech SE vaccine to Bangladesh and 4.7 million doses to Pakistan, CNN reported earlier on Wednesday, citing a White House official.
The Biden administration had previously vowed to donate a second tranche of 500 million doses to the COVAX global vaccine sharing program, raising its total pledge to some 1.2 billion COVID vaccine doses, with the latest batch expected to start shipping this month.
Global health experts have said at least 5 billion to 6 billion doses are needed by poorer countries to help protect them against the coronavirus amid the ongoing pandemic.
Overall COVAX, backed by the World Health Organization and the Global Alliance for Vaccines and Immunization, has delivered more than a billion doses to 144 countries and aims to achieve 70% COVID-19 immunisation coverage by mid-2022.
Health experts have criticised rich countries for not doing enough to make COVID-19 vaccines more accessible, singling out the United States in particular for pushing booster shots for fully vaccinated Americans while much of the world's population awaits first shots.
Experts and leaders from developing nations have also warned that vaccine hoarding by wealthy nations could lead to the emergence of new concerning coronavirus variants.
The White House on Wednesday defended its efforts, saying it had shipped more free doses than any other nation.
"Put America's leadership into perspective. We have shipped four times more free doses to the world than any other country," Zients told reporters.