The United States on Monday began administering the first doses of the COVID-19 vaccine, in a much-awaited moment for the country that has suffered the world's highest numbers of coronavirus cases and deaths.

The vaccine, developed by U.S. pharmaceutical giant Pfizer Inc. and its German partner BioNTech SE, was granted an emergency use authorization by U.S. regulators on Friday for individuals aged 16 or older.

Britain last week became the first Western nation to start a mass effort to inoculate people against COVID-19, the respiratory illness caused by the novel coronavirus, using the same Pfizer-BioNTech vaccine. Japan is also among the countries that have a contract to receive a supply of the vaccine.

A health care worker in New York was seen getting a shot in live news coverage, becoming one of the first to receive the vaccine that is being shipped across the United States. Frontline workers and residents of nursing homes are to be vaccinated first.

The vaccine is administered as a two-dose series, with three weeks between the shots. The duration of protection against the disease is currently unknown, according to U.S. regulators.

Individuals with a severe allergic reaction to any of the vaccine's ingredients should not get the shots. As for pregnant women and those who are immunocompromised, vaccine providers will need to consider each case individually, they said.

Concerns appear to linger among the public as to whether the vaccine, developed in the remarkably short span of less than a year, is safe enough despite assurances from regulatory authorities that there was no cutting of corners amid political pressure.

More than 72 million cases of COVID-19 have been confirmed around the world, with the death toll topping 1.6 million, according to a tally by Johns Hopkins University.

In the United States, more than 16 million people have been infected and around 300,000 have died due to the pandemic that has accelerated in the country since March.

The Japanese government has an agreement with Pfizer to receive a supply of 120 million vaccine doses, enough for 60 million people, or roughly half its population, in the first half of next year.

Japan also has an agreement with U.S. biotechnology firm Moderna Inc., which has also filed for vaccine use authorization in the United States, for enough vaccine doses to cover 25 million people starting in the first half of next year.