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

White House press secretary Jen Psaki says the Biden administration is planning to send 2.5 million doses to Mexico and 1.5 million to Canada as a “loan.”

The AstraZeneca vaccine has not been authorized for use in the U.S. but has been authorized by the World Health Organization. The premier of Ontario, Doug Ford, thanked Biden for his willingness to share the vaccines.

Canadian regulators have approved the Pfizer, Moderna, AstraZeneca and Johnson & Johnson vaccines, but acquiring them has proven difficult. Canada ranks about 20th in the number of doses administered, with about 8% of the adult population getting at least one shot. That compares with about 38% in the U.K. and 22% in the U.S.

Mexico has fully vaccinated more than 600,000 people and more than 4 million have received a single dose in a country of 126 million.