President Joe Biden is delaying a target date for overseas shipments of 80 million doses of coronavirus vaccines donated by the U.S., with millions of shots produced by AstraZeneca Plc still in a safety review.

Biden's White House on Monday announced a list of countries that would receive 55 million doses, after previously detailing the first tranche of 25 million. In total, three-quarters of the 80 million will be sent through COVAX, a World Health Organization-backed vaccine procurement effort.

The announcement, however, dials back the initial U.S. commitment. Biden once said he'd "send” 80 million doses by the end of June, and is now pledging only to "allocate" them by then, suggesting shipments will stretch into July or beyond.

The delay is due in part to a stockpile of 60 million AstraZeneca doses that he'd planned to donate, and that were meant to make up the bulk of the 80 million. However, those vaccines remain under U.S. Food and Drug Administration review.

(With input from agencies)