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.