The US Food and Drug Administration on Saturday authorised Johnson & Johnson’s single-shot Covid-19 vaccine for emergency use, beginning the rollout of millions of doses of a third effective vaccine that could reach Americans by early next week.

The announcement arrived at a critical moment, as the steep decline in coronavirus cases seems to have plateaued and millions of Americans are on waiting lists for shots.

Johnson & Johnson has pledged to provide the US with 100 million doses by the end of June. When combined with the 600 million doses from the two-shot vaccines made by Pfizer-BioNTech and Moderna slated to arrive by the end of July, there will be more than enough shots to cover any American adult who wants one.

But federal and state health officials are concerned that even with strong data to support it, some people may perceive Johnson & Johnson’s shot as an inferior option.

The new vaccine’s 72 per cent efficacy rate in the US clinical trial site — a number scientists have celebrated — falls short of the roughly 95 per cent rate found in studies testing the Moderna and Pfizer-BioNTech vaccines. Across all trial sites, the Johnson & Johnson vaccine also showed 85 per cent efficacy against severe forms of Covid-19 and 100 per cent efficacy against hospitalisation and death.

“Don’t get caught up, necessarily, on the number game, because it’s a really good vaccine, and what we need is as many good vaccines as possible,” Dr Anthony S. Fauci, the government’s top infectious disease expert, said in an interview on Saturday. “Rather than parsing the difference between 94 and 72, accept the fact that now you have three highly effective vaccines. Period.”

If Johnson & Johnson’s vaccine would have been the first to be authorised in the US instead of the third, “everybody would be doing handstands and back flips and high-fives”, said Dr James T. McDeavitt, dean of clinical affairs at the Baylor College of Medicine.

On Sunday a committee of vaccine experts who advise the Centres for Disease Control and Prevention will meet to discuss whether certain population groups should be prioritised for the vaccine, guidance that state health officials have been eagerly awaiting in anticipation of the FDA’s authorisation.

One administration official familiar with the distribution of the vaccine said that shipments would begin on Monday and deliveries could arrive as soon as Tuesday.

Johnson & Johnson has said it will ship nearly four million doses as soon as the FDA authorises distribution and another 16 million or so doses by the end of March. That is far fewer than the 37 million doses called for in its $1 billion federal contract, but the contract says that deliveries that are 30 days late will still be considered timely.

The federal government is paying the firm $10 a dose for a total of 100 million doses to be ready by the end of June, substantially less per dose than it agreed to pay Moderna and Pfizer, which developed its vaccine with a German partner, BioNTech.

Johnson & Johnson’s one-dose vaccine will allow states to rapidly increase the number of people who have been fully inoculated. Unlike the other two vaccines, it can be stored at standard refrigeration temperatures for at least three months.

New York Times News Service