The one-shot coronavirus vaccine made by Johnson & Johnson provides strong protection against severe disease and death from Covid-19, and may reduce the spread of the virus by vaccinated people, according to new analyses posted online by the Food and Drug Administration on Wednesday.
The vaccine had a 72 percent overall efficacy rate in the United States and 64 percent in South Africa, where a highly contagious variant emerged in the fall and is now driving most cases. The efficacy in South Africa was seven points higher than earlier data released by the company.
The vaccine also showed 86 percent efficacy against severe forms of Covid-19 in the United States, and 82 percent against severe disease in South Africa. That means that a vaccinated person has a far lower risk of being hospitalized or dying from Covid-19.
The analyses confirmed that Americans are likely to benefit soon from a third effective coronavirus vaccine developed in under a year, as demand for inoculations greatly outstrips supply. The F.D.A. could authorize the vaccine as early as Saturday, depending on a vote of its vaccine advisory panel on Friday after it discusses the newly released documents.
“With a J&J vaccine, we’ll be able to accelerate the vaccine rollout for our country and for the world,” said Dan Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston who led much of the early research on the vaccine last year.
Johnson & Johnson’s vaccine can be stored at normal refrigeration temperatures for at least three months, making its distribution considerably easier than the authorized vaccines made by Moderna and Pfizer-BioNTech, which require two doses and must be stored at frigid temperatures.
But access to the new vaccine could be severely limited at first. Dr. Richard Nettles, the vice president of U.S. medical affairs at Janssen Pharmaceuticals, the drug development arm of Johnson & Johnson, told lawmakers on Tuesday that nearly four million doses would be ready for shipment after the F.D.A. authorizes the vaccine, far below the 12 million it had originally pledged to give the federal government by the end of February.
White House officials had an even lower estimate on Tuesday, telling governors on a weekly call that around two million doses would be available next week, according to an administration official.
Dr. Nettles said on Tuesday that a total of 20 million doses would be ready by the end of March. The company has a contract to deliver 100 million doses by the end of June.
Johnson and Johnson’s vaccine has a lower efficacy rate than the vaccines from Moderna and Pfizer-BioNTech, which are both around 95 percent.
But in South Africa, the Johnson & Johnson vaccine is so far the clear winner. Novavax’s shot had an efficacy of 49 percent in South Africa. And a small trial in South Africa of the AstraZeneca-Oxford vaccine found that it did not offer much protection at all. The negative results led the South African government to abandon its plan of giving a million doses of AstraZeneca vaccines to health care workers. Last week, the government started giving Johnson & Johnson’s vaccines instead, and has so far administered more than 32,000.
The newly released documents, which include the F.D.A.’s first technical analysis of the company’s 45,000-person clinical trial, presented evidence that the vaccine was safe, with noticeably milder side effects than the Pfizer and Moderna vaccines and without any reports of severe allergic reactions like anaphylaxis.
The vaccine’s protection was consistent across Black, Hispanic and white volunteers, and also across different ages. The trial indicated a lower efficacy, of 42.3 percent, for people over 60 who had risk factors like heart disease or diabetes. But this figure came with a large amount of statistical uncertainty, the F.D.A. noted.
Although several vaccines can protect people from getting sick with Covid-19, it is unclear whether the shots can also prevent people from getting infected and passing the virus to others, leading to a debate about how quickly society can return to normal after inoculations begin.
Moderna’s trial found some hints that vaccinated people were less likely to develop an infection without symptoms. And AstraZeneca found that its vaccine reduced asymptomatic infections by about half.
Johnson & Johnson looked for asymptomatic infections by checking for coronavirus antibodies 71 days after volunteers got a vaccine or a placebo. The new analyses estimate that the vaccine has an efficacy rate of 74 percent against asymptomatic infections. But that calculation was based on a relatively small number of volunteers, and the F.D.A. noted that “There is uncertainty about the interpretation of these data and definitive conclusions cannot be drawn at this time.”
“I think it’s going to add to the growing evidence that the vaccines really do prevent infection as well as prevent disease,” Dr. Barouch said.