Mexico and Canada are at the top of President Joe Biden’s list of countries to eventually receive exports of U.S.-made coronavirus vaccines, according to a U.S. official familiar with the plans.

But Biden and administration officials have said the U.S. will not share its vaccines until after it has enough for its own people, leaving timing for any exports unclear.

The U.S. has raced ahead of most of the rest of the world in vaccinating its population under Biden, who has focused on ramping up both supply and locations where Americans can obtain shots. He has meanwhile spurned requests from other countries to share the U.S vaccine supply, which includes millions of doses of a shot by AstraZeneca Plc that has yet to be authorized for use in the country.

Mexico this week made its second public request for the U.S. to share doses, specifically asking for shots from the as-yet untapped AstraZeneca supply.

The U.S. continues to evaluate how it will proceed but Mexico and Canada are at the front of the line line for vaccine exports, the official said Wednesday. The official asked not to be identified because a decision hasn’t been made.

Biden said Tuesday that he’s in talks with countries about sharing vaccines, but he didn’t name them. “I’ve been talking with several countries already. I’ll let you know that very shortly,” Biden said.

White House Press Secretary Jen Psaki said March 1 that the U.S. is focused on securing enough vaccines for its own people, but signaled that North American economic recovery would be a priority as it begins exports.

“The next step is economic recovery, and that is ensuring that our neighbors, Mexico and Canada, have similarly managed the pandemic so that we can open our borders and build back better,” she said.

On March 12, Psaki said the U.S. had received requests from several countries for vaccines and had so far denied them.

“At this time, there have been requests around the world, of course, from a number of countries who have requested doses from the United States, and we have not provided doses from the U.S. government to anyone,” she said.

The U.S. has firm orders for enough vaccines for 500 million people from Pfizer Inc., Moderna Inc. and Johnson & Johnson. It has also ordered enough shots for another 150 million people from AstraZeneca, though the company hasn’t yet sought FDA authorization for its vaccine.

AstraZeneca has nonetheless begun manufacturing doses of its vaccine in the U.S. in anticipation of eventual FDA clearance.

The White House has said it is securing extra doses because of uncertainty both over which shot will be best for use in children and whether adults will need booster shots.

“We also want to make sure we have maximal flexibility, that we are oversupplied and over-prepared, and that we have the ability to provide vaccines -- whatever the most effective ones are -- to the American public,” Psaki said on March 12.