The US Food and Drug Administration on Monday fully approved the Pfizer-BioNTech Covid vaccine, a move expected to trigger a new wave of vaccine mandates as the Delta variant batters the country.

Around 52 percent of the country is fully vaccinated, but health authorities have hit a wall of vaccine hesitant people, impeding the national campaign.

"The FDA's approval of this vaccine is a milestone as we continue to battle the Covid-19 pandemic," acting FDA Commissioner Janet Woodcock said in a statement.

"While all three COVID vaccines have met FDA's strict standards for emergency use, this FDA approval should give added confidence that this vaccine is safe and effective. If you're not vaccinated yet, now is the time," tweeted President Joe Biden.

The vaccine, which will now be marketed under its brand name Comirnaty, is the first to receive full approval.

More than 200 million shots have already been administered under an emergency use authorization (EUA) that was granted on December 11, 2020.

The decision to approve it among people aged 16 and up was based on updated data from the drug's clinical trial, which found the vaccine more than 90 percent effective in preventing Covid.

"Overall, approximately 12,000 recipients have been followed for at least six months," the FDA said in its statement.

Most commonly reported side effects included pain, redness and swelling at the injection site, fatigue, headache, muscle or joint pain, chills and fever.

The FDA is continuing to investigate safety data regarding myocarditis (heart inflammation), particularly within seven days after the second dose. The data so far shows an increased risk among males under 40 compared to females and older males.

The highest risk has been detected in boys aged 12 through 17, with available data suggesting most individuals recover but some require intensive care.

The US military said shortly after the announcement that it would mandate the vaccine, and a slew of private businesses and universities are expected to follow.

Immediately after the announcement, New York City said it would require all its department of education employees to receive at least one dose of vaccine by September 27, without the option for regular testing instead.

The vaccine remains available under emergency use authorization to children aged 12 to 15, but because it has now been fully approved, physicians may prescribe it to children under 12 if they believe it will be beneficial.

Blow to anti-vaxxers

"One of the talking points of the anti-vaccine movement which has falsely claimed that this was an 'experimental vaccine' has been removed," Amesh Adalja of the Johns Hopkins University Center for Health Security told AFP.

"Hopefully now you'll see people who said that they were waiting for full approval line up to get vaccinated, hopefully more organizations, more businesses will require the vaccine as a condition of employment as a condition of participation."

A recent survey by the Kaiser Family Foundation found 30 percent of adults said full approval would make them more likely to get vaccinated.

It comes as the ultra-contagious Delta variant pummels the country, with new cases and hospitalizations approaching levels last seen during the winter wave.

The hardest hit regions include southern states Florida, Alabama, Mississippi and Louisiana.

The number of people rolling up their sleeves for a shot has risen in these states in recent weeks, but the national rate is still well below its peak from spring.

Some 628,000 people have died from coronavirus infection in the United States, making it officially the hardest hit country in the world -- though experts say it is possible that India may in fact hold the record.

Vaccines are less effective against the Delta variant than they were against previous strains, particularly against infection, making the goal of high population level vaccination critical.

The Biden administration announced last week plans to make a booster shot immediately available for immunocompromised individuals, and recommended all vaccinated people get a third shot eight months after their second.