Mr. Biden has a week and a half to meet his deadline, a task made more hard as the administration tries to change which manufacturers' vaccines would be included in the 55 million portion.
A large number of poorer countries receiving vaccines through a global sharing scheme did not have enough doses to continue programmes, the World Health Organization added.
Where the doses are going: Most will be sent to countries in Latin America and the Caribbean, Asia and Africa.
President Joe Biden has promised that the US will be the vaccine arsenal for the world to help end the pandemic, though poorer countries have pressed the USA and other wealthy nations to do more as they struggle to secure vaccines.
The big picture: President Biden and G7 leaders have pledged to send 1 billion doses to the developing world, including 500 million from the US alone.
On a continental level, only 40 million doses have been administered so far in Africa - less than 2% of the population, Mr Ramaphosa said.
The White House said it is still working through a variety of logistical and regulatory issues involved in shipping vaccine overseas, like safely transporting the doses and, at times, having to send related supplies, like syringes and alcohol pads, along with them.
The first tranche included the Johnson & Johnson, Moderna and Pfizer/BioNTech vaccines, but it was not immediately clear what the second tranche would comprise.
The 55 million doses will be taken from the US supply of Pfizer Inc, Moderna Inc, and Johnson & Johnson shots, though if AstraZeneca's vaccine gets a green light from the Food and Drug Administration, it would likely be added to the mix as well.
Uganda, Zimbabwe, Bangladesh and Trinidad and Tobago are just some of the countries that have reported running out of vaccines in recent days.
Approximately 41 million of the 55 million doses will be shared through COVAX, with 14 million for Latin American and Caribbean countries, 16 million for Asia, 10 million for Africa.
The White House said it wanted the doses to be prioritized for health care workers and those who are most at risk.
Worldwide partners are eager to get US help.
The White House added that countries that would receive the vaccine through direct sharing are Nigeria, Kenya, Ghana, South Africa, Egypt, Colombia, Argentina, Haiti, Dominican Republic, Costa Rica, Panama, Afghanistan, Bangladesh, Pakistan, Philippines, Vietnam, Indonesia and many others.