An external committee of scientific experts is scheduled to meet Friday to recommend whether the FDA should authorize the shot

A Food and Drug Administration review released Wednesday of the single-shot coronavirus vaccine made by pharmaceutical giant Johnson & Johnson found it was safe and effective and completely prevented hospitalizations and deaths in a large clinical trial.

The review sets the stage for a third coronavirus vaccine to be authorized as soon as this weekend, a point of hope in the middle of a pandemic that has killed more than a half-million people in the United States.

The review, although positive, was more nuanced than regulators’ assessments of the first two coronavirus vaccines, reflecting a pandemic that has entered a more complicated phase as variants capable of slipping by some aspects of immunity have emerged. The Johnson & Johnson vaccine was more than 85 percent effective at preventing severe illness, including in a region dominated by a concerning variant, but only 66 percent protective overall when moderate cases were included.

The FDA scientists found that the “known benefits” of the vaccine included reducing the risk of symptomatic and severe cases of its disease, covid-19, at least two weeks after vaccination. The review found vaccine efficacy against severe covid-19 “was similarly high across the United States, South Africa, and Brazil.”

“We know this vaccine prevents 85 percent of the severe disease. . . . It was 100 percent effective in preventing hospitalization and deaths, and that’s really what’s important,” said Nancy M. Bennett, a professor of medicine and public health sciences at the University of Rochester School of Medicine and Dentistry. “Those facts are the most important thing to recognize.”

The vaccine was less effective in a subgroup of adults older than 60 who also had risk factors for severe illness, but regulators noted there were no deaths or cases requiring medical intervention a month after those older adults received vaccines. Overall, there were seven deaths in the trial, all in the group that received a placebo.

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An external committee of scientific experts is scheduled to meet Friday to recommend whether the FDA should authorize the shot. If the regulatory deliberations follow the path of the previous two authorized coronavirus vaccines — a joint vaccine from U.S. pharmaceutical giant Pfizer and German biotech firm BioNTech, and one from U.S. biotech company Moderna — a decision could come this weekend.

Public health officials have eagerly awaited the arrival of the Johnson & Johnson vaccine because it is expected to streamline the logistics of a complicated mass vaccination campaign. The vaccine can be stored in a refrigerator for several months, which should ease the challenges of distributing frozen products, and it doesn’t require a follow-up visit for a booster shot.

Creating a new vaccine can involve thousands of people over several years. Here's what it takes to produce a new FDA-approved vaccine. (John Farrell/The Washington Post)
The FDA advisory committee will consider the Johnson & Johnson vaccine at a “very tenuous time,” said Nahid Bhadelia, an infectious-disease doctor at Boston Medical Center. “Nobody knows how to feel.” While hospitalizations and deaths related to covid-19 are declining, there are concerns that variants could spoil the improving picture.

The Johnson & Johnson results highlight the challenge variants pose to all of the vaccines: The large, international trial found the vaccine was 72 percent effective at preventing cases of moderate to severe covid-19 in the United States, where variants of concern have only recently begun to be detected. But in South Africa, where a variant capable of evading some parts of immunity became dominant late last year, it was 57 percent effective against moderate to severe illness.

But the results also underscore a reassuring message: The immunity from the vaccine will prevent people from the worst outcomes, even if it allows some cases of coughs and fevers to slip by. The vaccine was 89 percent effective at preventing severe illness in South Africa.

The FDA, which on Monday issued new guidance to manufacturers on how to deal with variants, plans to brief the advisory committee Friday on the importance of getting ready for possible updates to vaccines. To streamline the process for getting clearance for modified vaccines, the FDA said, companies will be able to submit smaller studies testing immune responses in people’s bodies rather than lengthy, large trials in which researchers give half the participants a placebo and wait to see if people get sick or not.

Several manufacturers, including Johnson & Johnson, are studying potential modifications to their vaccines to counter variants such as those first detected in the United Kingdom and South Africa.

The vaccine appears to have met the safety and efficacy criteria laid out by the agency — efficacy of at least 50 percent and two months’ worth of follow-up safety data.

If an emergency use authorization is granted, about 2 million doses will be available to ship starting next week to states and other jurisdictions, according to two federal officials familiar with the situation who spoke on the condition of anonymity because they were not authorized to speak publicly. Supply will ramp up to 20 million doses by the end of March.

But public health experts have also expressed concerns that the public may compare vaccines tested under starkly different circumstances and make judgments about which one they should receive. In Europe, the less-spectacular data supporting the vaccine developed by the University of Oxford and British-Swedish pharmaceutical firm AstraZeneca has led to societal debate over whether people should defer vaccination until they can get one of the other shots, from Pfizer-BioNTech or Moderna.

“We have a really important job to do on how we message this,” said E. John Wherry, an immunologist at the University of Pennsylvania. “The day that an individual has a choice on which vaccine to get — that’s a great day, but probably won’t be until summer.” Until then, he said, people should take the vaccine they can get, because all are robustly effective.

Isaac Stanley-Becker contributed to this report.

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