THE US IS getting a third vaccine to prevent Covid-19, as the Food and Drug Administration cleared a Johnson & Johnson shot that works with just one dose instead of two.

Health experts are anxiously awaiting a one-and-done option to help speed vaccinations, as they race against a virus that already has killed more than 510,000 people in the US and is mutating in increasingly concerning ways.

The FDA said J&J’s vaccine offers strong protection against what matters most: serious illness, hospital admissions and death.

One dose was 85% protective against the most severe Covid-19 illness, in a massive study that spanned three continents — protection that remained strong even in countries such as South Africa, where the variants of most concern are spreading.

“The more vaccines that have high efficacy that we can get into play, the better,” Dr Anthony Fauci, the top US infectious disease expert, said ahead of the FDA’s ruling.

President Joe Biden said the “exciting news for all Americans” was an “encouraging development in our efforts to bring an end to the crisis”.

“But I want to be clear: this fight is far from over,” he added, encouraging people to stick with masks and other public health measures.

Shipments of a few million doses to be divided among states could begin as early as Monday. By the end of March, J&J has said it expects to deliver 20 million doses to the US, and 100 million by summer.

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

There are clear advantages aside from the convenience of one shot.

Local health officials are looking to use the J&J option in mobile vaccination clinics, homeless shelters, even with sailors who are spending months on fishing vessels. It is suited to communities where it is hard to be sure someone will come back in three to four weeks for a second vaccination.

The J&J vaccine also is easier to handle, lasting three months in the refrigerator compared to the Pfizer and Moderna options, which must be frozen.

Worldwide, the company aims to produce about one billion doses globally by the end of the year. On Thursday, the island nation of Bahrain became the first to clear its use.