The US drug regulator has granted full approval to the Pfizer/BioNTech Covid-19 vaccine, making it the first to secure such Food and Drug Administration validation as health authorities struggle to win over vaccine sceptics.

The FDA, which gave the two-dose vaccine emergency-use authorisation in December, gave its full approval for use in people age 16 and older based on updated data from the companies' clinical trial and manufacturing review.

Public health officials hope the action will convince unvaccinated Americans that Pfizer's shot is safe and effective.

There is entrenched vaccine scepticism among some Americans,p articularly conservatives. Covid-19 cases, driven by the highly infectious Delta variant, have surged in parts of the United States with lower vaccination levels.

"This FDA approval should give added confidence that this vaccine is safe and effective," President Joe Biden, who has sought to increase vaccination levels, wrote on Twitter.

Shortly after the FDA's announcement, the Pentagon said it is preparing to make the vaccine mandatory for US military personnel.

US health officials expect that the FDA's full approval also will prompt more state and local governments, as well as private employers, to impose vaccine mandates.

"While millions of people have already safely received Covid-19 vaccines, we recognise that for some, the FDA approval of a vaccine may now instill additional confidence to get vaccinated," said Janet Woodcock, the FDA's acting commissioner.

More than 204 million people in the United States have received the Pfizer vaccine.

The FDA's approval extends the shelf life of Pfizer shots from six months to nine months.

It also confirms that the vaccine increases risk of heart inflammation, particularly among young men in the week following their second shot.

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The approval makes it easier for physicians to prescribe a third dose of Pfizer's vaccine off-label for people who may benefit from additional protection against Covid-19.

Pfizer shares were up around 2.5% and BioNTech shares were up more than 10%.

The two other Covid-19 vaccines given emergency-use authorisation - made by Moderna and Johnson & Johnson - have not yet received full FDA approval.

The FDA gave emergency-use authorisation to Pfizer's vaccine for people age 16 and older in December - making it the first shot to gain such backing in the United States - and gave further emergency-use authorisation for people age 12 and up in May.

Pfizer and BioNTech said they plan to apply for full approval in children ages 12 to 15 as soon as required data is available.

Ms Woodcock said the FDA is not recommending that children under age 12 get the vaccine now because it needs to ensure it is safe for them, telling reporters it "would be a great concern if people vaccinate children because we don't have the proper data."

Pfizer is expected to submit data this fall to support the shot's emergency-use authorsation for children under 12 based on smaller doses.

The American Academy of Pediatrics, representing children's doctors, discouraged having children under 12 receive the vaccine.

Pfizer's shot has received conditional regulatory approval elsewhere including the European Union and Britain.

The United States leads the world in reported Covid cases and deaths.

More than 625,000 Americans have died from the disease, including an average of more than 600 daily in recent weeks.

According to the Centers for Disease Control and Prevention, 71% of Americans age 12 and older - the population eligible to receive Covid-19 vaccines - have gotten at least one dose and 60.2% are fully vaccinated.

For the entire population, including children up to age 11 for whom no vaccines are yet approved, 60.7% of Americans have received at least one dose and 51.5% of them are fully vaccinated.

NYC orders teachers to get vaccine

New York City will require public school teachers and staff to get vaccinated against Covid-19, Mayor Bill de Blasio said today.

It is part of a push to get more residents vaccinated and slow the spread of the highly contagious Delta variant.

All 148,000 staff members in the United States' largest school district must get at least one dose of a vaccine by 27 September as part of the mandate, Mr de Blasio said.

In a first for city employees, Department of Education staff will no longer have the option to submit to weekly testing instead.

US educators and parents have been grappling with how to keep schools safe and open as the country battles another coronavirus surge