The White House on Monday announced where the U.S. would send 55 million additional COVID-19 vaccine doses allocated for other countries.

The Biden administration had already committed these doses as part of a pledge to allocate 80 million by the end of June, and an initial 25 million doses, announced earlier this month, have "begun shipping," the White House said. 

Officials gave more details Monday on where the remaining 55 million doses would be headed and the timeline for their shipment. 

The White House had previously said it would "send" 80 million doses by the end of June, but on Monday it said it would "allocate," but not necessarily have the shipments on their way by that time. Asked about the delay, White House Press Secretary Jen Psaki said logistical hurdles, not the supply of doses, is at issue. 

"What we've found to be the biggest challenge is not actually the supply, we have plenty of doses to share with the world, but this is a Herculean logistical challenge and we've seen that as we've begun to implement," Psaki said, pointing to issues of sharing "safety and regulatory information," and ensuring proper storage and temperature requirements. 

About 41 million will be shared through COVAX, the World Health Organization-backed program to equitably distribute doses worldwide. About 14 million of those will go to Latin America and the Caribbean. About 16 million will go to Asia, including India, Nepal, Bangladesh, Pakistan, Sri Lanka, Afghanistan, Maldives, Bhutan, Philippines, Vietnam, Indonesia, Thailand, Malaysia, Laos, Papua New Guinea, Taiwan, Cambodia and the Pacific Islands.

About 10 million will go to Africa, for countries "selected in coordination with the African Union."

Another 14 million doses will be shared outside of COVAX, with "regional priorities and other recipients." Those countries include Colombia, Argentina, Haiti, Afghanistan, Pakistan and Iraq. 

The White House cautioned that the shipments of vaccine doses "will take time," and said that while the doses are allocated by the end of June, they will not necessarily ship by then.  

"The specific vaccines and amounts will be determined and shared as the administration works through the logistical, regulatory and other parameters particular to each region and country," the White House said in Monday's announcement.  

Under pressure to do more to boost the global vaccine effort, President Biden announced earlier this month a larger donation of 500 million Pfizer doses, which will ship between August and the first half of next year. 

Experts have also stressed the need to boost manufacturing capacity, not just donate doses that are already being made.  

The White House noted Monday that through a U.S. partnership with Japan, Australia and India, and through the International Development Finance Corporation, more than 1 billion doses will be produced in Africa and India this year and next.