THE US is sending abroad AstraZeneca-Oxford vaccine it cannot use - because its regulatory system has not yet approved its use.

The US has already shared over 4 million doses of its AstraZeneca vaccine with Canada and Mexico.

At the end of April the US said it would provide 60 million doses of their AstraZeneca vaccine overseas, once it clears federal safety reviews.

Now President Joe Biden has confirmed that another 20 million doses of vaccines from Pfizer Inc., Moderna Inc. or Johnson & Johnson, will be shared on top of the AstraZeneca Plc he had already planned to give to other countries.

Mr Biden has been under global pressure to share his country's vaccines, but he had insisted that he had to first control the pandemic at home.

At the end of April, AstraZeneca said it had intended to seek US authorisation for the in the “coming weeks”. It had been expected by mid-April.

While delivering its first quarter financial results, at the end of April, it emerged the company delivered 68 million doses of the vaccine to the European Union, United Kingdom and other countries in the first three months of the year.

The company had said it was continuing to work on its application to US's Food and Drug Administration for emergency-use authorisation noting the “substantial size of the file" that will include data from US trials as well all other studies completed so far and real-world data collected from use of the vaccine in other countries.

It now looks extremely unlikely that Americans will get the AstraZeneca shot, even though the US had ordered 300 million doses of the vaccine in a $1 billion deal.

The nation at the end of April was on track to have enough doses for every adult by the end of May with only the three already-authorized vaccines - Pfizer, Moderna and Johnson & Johnson.

READ MORE: Coronavirus vaccine: Under-40s to be offered AstraZeneca alternative as latest blood clot data emerges

Jen Psaki, White House press secretary, said the new doses would go “to help countries battling the pandemic”.

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He added: “We are waiting for, of course, AstraZeneca, as you know, to go through the approval process of the FDA, but this will put 80 million doses out into the world by the end of June."

Among issues that AstraZeneca would have had to address are indications that the vaccine was linked to rare blood clots, particularly in younger people.

The India government on Monday said it identified 26 potential cases of bleeding and blood clotting due to the admnistration of the vaccine.

Several countries recommended that the vaccine only be given only to older people because of the link to the rare clots - known as CVSTs (cerebral venous sinus thrombosis).

Last month the UK's Joint Committee on Vaccination and Immunisation (JCVI), which advises how vaccines should be used, recommended healthy people under 30 be offered a different vaccine.

Vaccine experts say the blood clots are very rare and less than the blood clot risks of women taking birth control.

They say that for the vast majority of people the benefits of the vaccine vastly outweighs the risks.

By the end of April, according to the UK medical regulator, the MHRA, 79 cases were identified, and 19 people died.

This was out of a total of more than 20 million doses of the AstraZeneca vaccine which has been given in the UK at that time.

Some believe AstraZeneca may skip asking the FDA for emergency-use authorisation and instead pursue the more time-intensive application for a full-fledged licence.

Meanwhile Mexico's president Andres Manuel Lopez Obrador said last month that the country expects about another five million AstraZeneca doses from the US.

Approximately 2.7 million doses of AstraZeneca vaccine was sent to Mexico from the US between late March and April.

None of the additional 60 million doses that was due to be sent to other countries at the end of April had been available to ship immediately.

Ten million had been filled into vials, awaiting regulatory safety testing.

Another 50 million were expected to be produced between May and June.

When AstraZeneca released data from its US vaccine trial on March 22, company officials said they expected to apply for FDA authorization in the first half of April.

Once the application is filed, an FDA advisory committee will publicly debate the evidence behind the shots before the agency decides whether to allow emergency use.

Ruud Dobber, an AstraZeneca executive vice president, said at the time that if the FDA authorizes the vaccine, the company would deliver 30 million doses immediately, followed by another 20 million within the first month.

The vaccine was developed by researchers at Oxford University, who licensed the technology to AstraZeneca in an effort to tap into the company’s global manufacturing and distribution capacity. AstraZeneca in turn authorizes other companies to produce the shots around the world.

More than 3.3million people worldwide have died of COVID-19, including more than 580,000 in the US.

Mr Biden said in his vaccine announcement: "We're taking an additional step, to help the world. We know America will never be fully safe until the pandemic that's raging globally is under control. No oceans wide enough. No walls high enough to keep us safe.

"Rampant disease and death in other countries can destabilize them, those countries and pose a risk to us as well. New variants could rise overseas that could put us at greater risk. And we need to help fight the disease around the world to keep us safe here at home and to do the right thing of helping other people. It's the right thing to do. It's the smart thing to do.

"It's the strong thing to do. In March, we shared over 4 million doses of our AstraZeneca vaccine with Canada and Mexico. At the end of April, we announced that we would provide another 60 million doses of our AstraZeneca vaccine overseas.

"Remember, this is the vaccine that's not authorized for use in the United States yet. So we're going to be sending it to folks once the FDA's reviewed this and said it's safe. This is all the AstraZeneca vaccine produced in the United States, all of it, will be sent to other countries."

The latest data showed that 60% of American adults had received at least one coronavirus vaccine dose Biden has set a goal of getting 70% of American adults at least partially vaccinated by July 4.

Many US allies had called on the Biden administration to send more vaccine doses to other countries, noting that the pandemic will not truly come to an end until vaccines are widely available around the world.

Mr Biden said last week that almost half of the world’s leaders had contacted his administration asking for help in getting access to more vaccine doses.

"We want to lead the world with our values, with this demonstration of our innovation and genuinity and the fundamental decency of the American people. Just as in World War II, America was the arsenal of democracy. In the battle against COVID-19 pandemic, our nation is going to be the arsenal of vaccines for the rest of the world," he said.

"We'll share these vaccines in the service of ending the pandemic everywhere. And we will not use our vaccines to secure favours from other countries. We'll work with Kovack, the International organization set up, and other partners to ensure that the vaccines are living in a way that is equitable and that follows the science and the public health data.

"Today's announcement, to share 80 million doses, is our next step as we ramp up the efforts to respond to COVID-19 around the world."