The figures were up from the more than 308 million doses the CDC said had been administered as of Saturday, out of over 374 million that had been doses delivered.
U.S. COVID-19 cases have dropped 95% since January. At least 65% of adults have had a least one vaccine shot. President Biden aims to have 70% of adults vaccinated with at least one shot by July 4.
Delta was first identified in India last fall, but was only designated a variant of concern by the World Health Organization in mid-May.
The donations will go through the COVAX vaccine program, led by WHO and GAVI, that distributes COVID-19 shots to low and middle-income countries.
"(Making) vaccines readily accessible to low- and middle-income countries is not an act of charity, but rather is in every country's strategic interest," the letter said.
Biden credited scientists, companies, the American people and his whole-of-government effort.
Vaccine diplomacy gets a little shot of corporatism
Whether or not Canada will actually need any doses of the J&J vaccine to complete its vaccination rollout is also up for debate.
The major milestone came with a caveat as vaccination rates slow and the so-called Delta variant continues to spread, prompting Biden to warn that infections could again rise if more Americans don’t roll up their sleeves.
The White House on Thursday formally announced its plan to purchase and donate 500 million doses of the Pfizer-BioNTech vaccine to 92 poorer countries and the African Union, dubbing it the “largest-ever purchase and donation of vaccines by a single country and a commitment by the American people to help protect people around the world from COVID-19.”
Biden to announce at the start of the G-7 summit that the U.S. will donate enough Pfizer COVID-19 vaccine to inoculate 250 million in poor countries.
COVID-19 Response Team Coordinator Jeff Zients said it's "more important than ever" for people to get vaccinated as the Delta variant spreads.