Johnson & Johnson's Janssen COVID-19 vaccine.
A vial of Johnson & Johnson's Janssen COVID-19 vaccine. Image Credit: REUTERS.

Johnson & Johnson's COVID-19 vaccine was endorsed on Friday by a panel of experts advising the Food and Drug Administration, clearing the last hurdle before a formal authorization expected on Saturday, according to two people familiar with the agency's plans. The nation's first shipments will go out in the days after that.

It will be the third shot made available to the United States in the year since the first surge of coronavirus cases began washing over the country, and it will be the first vaccine to require just one dose instead of two.

Johnson & Johnson's formulation worked well in clinical trials, particularly against severe disease and hospitalizations, even though it did not match the sky-high efficacy rates of the first two vaccines made by Pfizer-BioNTech and Moderna.

The panel, made up of independent infectious disease experts, statisticians and public health researchers, voted unanimously in favor of authorizing the vaccine.

"We're dealing with a pandemic right now," said Dr. Jay Portnoy, an allergist at Children's Mercy Hospital in Kansas City, Missouri, and a member of the board. "It's great that we have this vaccine."

During Johnson & Johnson's presentation to the panel, Dr. Gregory Poland, a virologist at the Mayo Clinic and a paid external consultant for the company, noted the vaccine's efficacy, ease of use and low rate of side effects. It "nearly checks all the boxes," he said. "To me, it is clear that the known benefits vastly outweigh the known risks."

The vaccine had an overall efficacy rate of 72% in the United States and 64% in South Africa, where a concerning variant emerged in the fall. The shot showed 86% efficacy against severe forms of COVID-19 in the United States, and 82% against severe disease in South Africa.

Those are strong numbers, but lower than the roughly 95% efficacy rates of Pfizer-BioNTech and Moderna's vaccines against mild, moderate and severe cases of COVID.

Johnson & Johnson's vaccine is a single dose and uses a different kind of technology than the authorized vaccines. And the scale and size of the Johnson & Johnson trial was vast, spanning eight countries, three continents and nearly 45,000 participants.

Although the vaccine works with one shot, studies are underway to determine if a second dose would increase its protective effects.