The White House is holding onto some doses of AstraZeneca Covid-19 vaccine so they can be given to Americans quickly if authorised by the US health regulator, a top administration official has said.

AstraZeneca has produced doses of its vaccine in the United States, where it has yet to be approved.

The vaccine developed with Oxford University has been authorised for use in the European Union and many other countries.

Reuters reported this week that US officials told the EU not to expect shipments of the shot from the United States anytime soon.

"We have a small inventory of AstraZeneca so, if approved, we can get that inventory out to the American people," White House Covid-19 response coordinator Jeffrey Zients said in a press call.

The New York Times reported this week that tens of millions of doses have already been produced in the United States and are sitting in production facilities unused.

AstraZeneca said in February it expects its vaccine could receive US emergency use authorisation at the beginning of April and could immediately deliver 30 million doses to locations around the United States.

The US stance could jeopardise AstraZeneca's attempts to come closer to delivering on its contractual obligation with the EU of 180 million doses in the second quarter.

AstraZeneca told the EU earlier this year it would cut its supplies in the second quarter by at least half to less than 90 million doses, EU sources told Reuters, after a bigger reduction in the first three months of the year.

US President Joe Biden said on Wednesday the government will first give Americans the  vaccines, but any surplus would be shared with the world.

"We...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," White House press secretary Jen Psaki told reporters.

"A number of countries... have requested doses from the United States and we have not provided doses from the U.S.government to anyone," she added.

The United States has been one of the world leaders in vaccine administration. It has distributed more than 130 million shots and administered nearly 100 million, according to federal data last updated on Thursday.

White House officials said on Friday that 65% of Americans over 65 years old have been given shots.

Meanwhile, the World Health Organization has approved the emergency-use listing of Johnson & Johnson's Covid-19 vaccine. 

It is third vaccine to receive the backing from the WHO.

The listing covers use in all countries and for roll-out of the vaccine platform COVAX and comes on the back of European Medicines Agency (EMA) authorisation announced on Thursday.

Germany has said it is not expecting to receive the newly approved Johnson & Johnson coronavirus vaccine until "mid-to-late April", health minister Jens Spahn has said, adding that the EU is querying the company over the delays.

However Mr Spahn warned that Germany would have to wait at least another month to receive the first doses from the US firm, as Berlin cited production issues and what amounted to a an effective US ban on exports of domestically produced vaccines.

"It's a pain with Johnson & Johnson. We have a European authorisation, but the deliveries will only be there from mid-to-late April at the earliest," said the minister at a weekly press conference in Berlin.

He added that the European Commission was in talks with the company over the problem. 

"We made an advance payment of €300m production and signed a contract in October, so we of course have to ask what has happened," he said. 

He said that Germany and the EU were now working on "short-term solutions" to the problem such as setting up production facilities in Germany.

Speaking about the issue later Friday, Angela Merkel's spokesman Steffen Seibert raised US reluctance to export doses as another problem for Europe's supply.

While European-produced vaccines were benefiting countries around the world, other countries like the US and UK were exporting "almost nothing", Mr Seibert said. 

"This is also something that the European Commission will discuss... with the companies and the governments of other countries," he added. 

It comes after AstraZeneca again angered the European Union by scaling back deliveries of Covid-19 vaccines, but got a boost when the World Health Organization dismissed blood clotting fears that have prompted countries in Europe and Asia to suspend use of the shot.

The EU has been much slower to start mass vaccination than the UK because of a slower approval and purchasing process and repeated supply hold-ups.

EU regulators have dismissed scattered reports of blood clots in people who had received the AstraZeneca vaccine, but Thailand has joined a handful of European countries in suspending use of the shot - the first and cheapest to be developed and launched at volume around the world.

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However, the European Medicines Agency has said this afternoon that severe allergies should be added to the possible side effects of the vaccine after likely links were found to a number of cases in Britain.

The EMA said it had "recommended an update to the product information to include anaphylaxis and hypersensitivity (allergic reactions) as side effects".

"The update is based on a review of 41 reports of possible anaphylaxis seen among around five million vaccinations in the United Kingdom," it said in the highlights of the EMA committee that assesses the risk of medications.

"After careful review of the data, (the committee) considered that a link to the vaccine was likely in at least some of these cases."

The EMA said however that anaphylaxis, or what it called "severe allergic reactions", was already what it called a "known side effect that may occur, very rarely, with vaccines".

The AstraZeneca vaccine's product information already said that people should be kept under "close observation for at least 15 minutes" after getting the jab in case of allergic reactions.

An AstraZeneca document dated 10 March, seen by Reuters and shared with EU officials, shows that the Anglo-Swedish drugmaker expects to have delivered 30 million doses to the EU by the end of March - 10 million less than it pledged only last month, and only a third of its contractual obligation.

A company spokesman declined to comment, but a person familiar with the situation said there had been difficulties with international supply chains.

Industry executives have warned of manufacturing problems as countries try to protect their own supplies of vaccines, ingredients and the equipment to make, bottle and transport them.

The United States has told Brussels that it will not allow AstraZeneca shots made in the United States to be exported in the near future, Reuters reported yesterday.

Last week Italy and the EU blocked a shipment of AstraZeneca vaccines from Italy to Australia, in the first application of a mechanism that allows the EU to refuse export requests from vaccine makers that break EU supply contracts.

The company has acknowledged production problems in the EU, but also said it expected to ship some output to the EU from the United States.

Its contract pledges "best reasonable efforts" to meet a target of 300 million doses for the EU by the end of June.

Brussels has become increasingly frustrated.

"I see efforts, but not 'best efforts'. That's not good enough yet," EU industry commissioner Thierry Breton tweeted yesterday.

Germany said it was talking to the US about missing shipments of Covid-19 vaccines, noting that more than 30 countries including the United States were receiving vaccines made in the EU.

The EU programme has also been upset in the last two weeks by the reports of blood clots.

Yesterday, Denmark and non-EU members Norway and Iceland suspended their use of the vaccine. Austria and Italy have stopped using specific batches.

But today the WHO said the vaccine was "excellent" and that no causal link had been established to the blood clots.

"It's very important to understand that, yes, we should continue to be using the AstraZeneca vaccine," spokeswoman Margaret Harris told a briefing.

"All that we look at is what we always look at: Any safety signal must be investigated."

AstraZeneca said yesterday it had found no evidence of increased risk of deep vein thrombosis in more than 10 million recipient records.

The EMA said on Wednesday that the number of clots reported in people who had received the AstraZeneca vaccine was no higher than in the general population.

Bulgaria said it would suspend use of the vaccine until it saw written guidance from the EMA, but German Health Minister Jens Spahn told reporters that his country was following the EMA guidance.

"Everything we know so far suggests that the benefits of the vaccine, even after every individual case reported, are greater than the risks, and that continues to be the case," he said.

Germany, the most populous country in the EU, is due to receive about six million doses from AstraZeneca by the end of April, the document seen by Reuters shows, with France getting 4.7 million and Italy 4.4 million.

"We are still in a phase of absolute scarcity," Mr Spahn said.

Sanofi, Translate Bio launch human trial of mRNA Covid-19 vaccine

Sanofi and TranslateBio said they had started a human trial of their mRNA Covid-19 vaccine candidate, the French drugmaker's second vaccine project, which follows a protein-based shot hit by a delay last year.

It is the latest vaccine candidate based on a new technology known as messenger RNA. Shots by Pfizer/BioNTech and Moderna were launched after clinical trials showed high efficacy rates.

Real-world data from the rollout of the Pfizer shot in Israel and Britain have also been encouraging.

Sanofi and Translate Bio expect interim results of the phase I/II study, which will enroll 415 healthy adults across 13 sites, during the third quarter.

Participants will receive either a single dose of the vaccine or two doses 21 days apart while three dose levels will be examined, the companies said.

Sanofi did not give further indication on the timeline of the project.

Last month, Sanofi and GlaxoSmithKline launched a new clinical trial of a protein-based Covid-19 vaccine candidate in a attempt to revive their efforts against the pandemic afte ra setback in December delayed the shot's launch.

To appease critics after the delay, Sanofi said earlier this year it agreed to fill and pack millions of doses of vaccines made by Pfizer/BioNTech and Johnson & Johnson.

Global coronavirus infections have exceeded 118 million.