Johnson & Johnson’s Vaccine Could Get F.D.A. Green Light on Saturday

The Food and Drug Administration’s vaccine advisory panel is holding an all-day meeting on Friday to consider whether the coronavirus vaccine made by Johnson & Johnson should be authorized by federal regulators.

The panel is expected to endorse the vaccine, meaning that the United States may have a third one authorized as early as Saturday.

Composed of independent infectious disease experts, statisticians and epidemiologists, the panel will hear presentations from top scientists at Janssen Pharmaceuticals, the drug development arm of Johnson & Johnson. Committee members will then discuss the technical components of the vaccine with them and regulators at the F.D.A.

The committee’s vote is expected to occur late Friday afternoon or early evening.

The meeting participants are equipped with analyses published online this week by the F.D.A. and the company that detail how the vaccine works — its success in preventing moderate and severe cases of Covid-19, hospitalizations and death, as well as the side effects it causes and how its efficacy varied in different regions of the world and among different groups of people.

According to the briefing documents, the vaccine had an overall efficacy rate of 72 percent in the United States and 64 percent in South Africa, where a concerning variant emerged in the fall and has spread to the United States. The vaccine showed 86 percent efficacy against severe forms of Covid-19 in the United States, and 82 percent against severe disease in South Africa.

None of the nearly 22,000 vaccinated people in the trial died of Covid-19.

When the panel met in December to consider the two-dose coronavirus vaccines made by Pfizer-BioNTech and Moderna, the sky-high efficacy rates of those shots led to a consensus and resounding votes to endorse them.

The discussion on Friday could be more complicated.

Johnson & Johnson’s vaccine is a single dose and uses a different kind of technology than the first two authorized vaccines. And the scale and size of the Johnson & Johnson trial was vast, spanning eight countries, three continents and 45,000 participants. That resulted in a large data set that is likely to prompt a more complex — and potentially splintered — discussion.

The F.D.A.’s analysis estimated that the vaccine has an efficacy rate of 74 percent against asymptomatic infections, which suggests that it may help reduce the spread of the virus by vaccinated people. That is likely to be one subject of discussion at the meeting, as the public and health authorities grapple with how vaccination should — or shouldn’t — change behavior when cases remain high.