The United States has approved Johnson & Johnson's COVID-19 vaccine, making it the third to be used in the country.

The Food and Drug Administration on Saturday (February 27), as per local time, cleared the Johnson & Johnson vaccine shot. Unlike most COVID-19 vaccines in use, it works with just one dose instead of two.

The FDA announced the emergency use authorization of the J&J vaccine for adults aged 18 and older following Friday’s unanimous endorsement by the agency’s panel of outside experts.

President Joe Biden hailed the move but cautioned Americans against celebrating too soon. "Things are still likely to get worse again as new variants spread," he said in a statement, urging people to continue washing their hands, wearing masks, and maintaining social distancing.

The death toll due to the virus has crossed 510,000 in the country. Health experts have been waiting for one-and-done option to speed up the vaccination process.

During the trials, the J&J vaccine was found to be 85 per cent effective against the most severe COVID-19 illnesses. There were very few serious side effects reported in the trial, which also offered preliminary evidence that the vaccine reduced asymptomatic infections.

“The more vaccines that have high efficacy that we can get into play, the better,” Dr. Anthony Fauci, the top US infectious disease expert, was quoted by PTI as saying ahead of the FDA order.

The shipments of millions of vaccine doses across the states will start from Monday. J&J estimated that about 20 million doses will be delivered to the US by the end of March. The number would reach 100 million by summer, it expects.

J&J also is seeking authorization for emergency use of its vaccine in Europe and from the World Health Organization.

The company aims to produce about 1 billion doses globally by the end of the year.