The U.S. is planning to send a combined 4 million doses of the AstraZeneca COVID-19 vaccine to Mexico and Canada in its first export of shots.

A White House official confirmed Thursday that the Biden administration is planning to send 2.5 million doses to Mexico and 1.5 million to Canada as a “loan.” The details are still being worked out.

The AstraZeneca vaccine has not been authorized for use in the U.S. but has been by the World Health Organization. Tens of millions of doses have been stockpiled in the U.S. should it receive emergency use authorization, sparking an international outcry that lifesaving doses could not be used overseas.

The White House has said President Joe Biden's priority is the vaccination of all Americans, but the official said Biden was authorizing the loan because the “virus knows no borders.”

The official spoke on the condition of anonymity to discuss the transaction before it was officially announced.