The Food and Drug Administration on Saturday authorized Johnson & Johnson’s single-shot COVID-19 vaccine for emergency use in the US, adding a third effective vaccine to the arsenal.  

The rollout of millions of doses of the vaccine is reported to reach Americans by early next week, AFP reported.

By the end of March, J&J has said it expects to deliver 20 million doses to the U.S., and 100 million by summer.

The announcement arrives at a critical moment when the steep decline in coronavirus cases seems to have plateaued and millions of Americans are on waiting lists for jabs.

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“The authorization of this vaccine expands the availability of vaccines, the best medical prevention method for Covid-19, to help us in the fight against this pandemic, which has claimed over half a million lives in the United States,” said acting Food and Drug Administration director Janet Woodcock, AFP reported.

In large clinical trials, the J&J vaccine’s efficacy against severe disease was 85.9% in the United States, 81.7% in South Africa, and 87.6% in Brazil.

Overall, among 39,321 participants across all regions, the efficacy against severe COVID-19 was 85.4%, but it fell to 66.1% when including moderate forms of the disease, AFP reported.

Crucially, analyses of various demographic groups revealed no marked differences across age, race, or people with underlying conditions.

Just days before the J&J vaccine received approval from the expert panel, the death toll in the US breached the 500,000 mark.

The J&J vaccine is the third to be greenlighted in the United States after Pfizer’s and Moderna’s were provisionally approved in December.

Over 65 million people in America have so far received at least one shot of either the Pfizer or Moderna vaccines — but unlike those, the J&J vaccine requires just one dose, and is stored at fridge temperatures, offering logistical and practical advantages.

The J&J shot is slightly less protective than Pfizer and Moderna’s two-shot regimens, which both have an efficacy of around 95% against all forms of COVID-19 from the classic coronavirus strain.

There was a hint, based on preliminary data, that the vaccine might be effective against asymptomatic infection — though J&J said it needs to do more research to confirm this.

The company has announced it aims to deliver a total of 20 million doses by the end of March, with 100 million by June — though the US is pushing to expedite that timeline.

The J&J vaccine uses a common-cold causing adenovirus, which has been genetically modified so that it can’t replicate, to carry the gene for a key protein of the coronavirus into human cells.