The United States is preparing to send millions of doses of the AstraZeneca coronavirus vaccine to help neighboring Mexico and Canada, the White House said Thursday.

President Joe Biden's press secretary, Jen Psaki, confirmed said that 2.5 million doses were being lined up for Mexico and 1.5 million for Canada. A total of seven million doses are stockpiled.

However, Psaki was vague on the timing.

"We are assessing how we can loan doses," she said. "It's not fully finalized yet. It's what we're working towards, to Canada and Mexico."

AstraZeneca is approved in both countries, but is still awaiting the FDA's green light for use in the United States.

According to Psaki, deliveries of vaccines to the United States' huge trading partners would be in the form of a loan, paid back by future AstraZeneca doses when Canada and Mexico have their own surpluses.

"Our first priority remains vaccinating the US population," she said, adding however that "the reality is the pandemic knows no borders."

Making sure US neighbors also have the pandemic controlled is a "mission critical step."

Mexico's foreign minister said Thursday that a deal had been struck following talks between Biden and President Andres Manuel Lopez Obrador.

The United States plans to send millions of AstraZeneca Covid-19 vaccines to Canada and Mexico
The United States plans to send millions of AstraZeneca Covid-19 vaccines to Canada and Mexico AFP / JOEL SAGET

More details would come out on Friday, Marcelo Ebrard tweeted, "because we are still working on it."

Mexico, a country of 126 million people, has recorded around 196,000 known Covid-19 deaths -- the world's third-highest toll. The United States has the highest toll at more than half a million people, but is also now leading the way in vaccinations.

Lopez Obrador has been a vocal critic of unequal access to coronavirus vaccines, saying it is "totally unfair" that some countries have yet to receive a single dose.

He has complained that Mexico has to import vaccine doses from Europe even though they are also produced in the United States.

The issue was on the agenda for a virtual summit between Lopez Obrador and Biden on March 1 whose main focus was on immigration.

Mexico began mass vaccination on December 24, starting with health workers, but is desperate for more supplies.

Several European countries briefly paused AstraZeneca use after reported side effects.

However, the World Health Organization says the vaccine poses no risk and on Thursday the EU drugs regulator declared it "safe and effective."

On Monday, Prime Minister Justin Trudeau urged Canadians to take it, likewise saying it was "both safe and effective."