Documents released by the Food and Drug Administration Wednesday indicate that Johnson & Johnson's COVID-19 vaccine is overall safe and highly effective against the most severe outcomes of the illness.
The favorable review comes two days before a panel of independent advisors to the FDA is scheduled to discuss the company's application for emergency use. It is widely expected that the Vaccine and Related Biological Products Advisory Committee, or VRBPAC, will vote to recommend authorization of the vaccine.
The FDA is not required to along with the panel's recommendation, but it usually does.
On Tuesday, five COVID-19 vaccine manufacturers, including Johnson & Johnson, told Congress that they're working to ramp up the rollout of vaccine doses over the coming weeks and months.
Assuming the FDA will authorize the Johnson & Johnson vaccine for emergency use, the company said it would be able to provide 20 million shots by the end of next month, with an additional 100 million doses over the summer.
The company reported results of its phase 3 clinical trials in late January, finding that in the U.S., the shot was 72% effective in preventing moderate to severe disease — essentially, keeping people out of the hospital and dying from Covid-19.
When the company looked just at the shot's effect on preventing severe disease, it was 85% effective.
Globally, however, the vaccine's effectiveness against moderate to severe disease was lower: 66%. That's due to a decrease in effectiveness against the variant first found in South Africa. In that country, the vaccine's effectiveness fell to 57%.
Side effects were generally limited to arm pain, headache and fatigue. No deaths were reported among study participants who received the vaccine, and no hospitalizations were reported after 28 days.
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Johnson & Johnson's vaccine, made in partnership with Janssen Pharmaceuticals, is given in a single shot; the other two vaccines in use from Moderna and Pfizer-BioNTech, require two doses, three to four weeks apart.
The Johnson & Johnson shot only requires basic refrigeration for storage.
It uses an inactivated virus, called an adenovirus, to teach the body's immune system to recognize and fight off SARS-CoV-2, the virus that causes Covid-19.
The vaccines made by Pfizer-BioNTech and Moderna use a different type of technology, using genetic material called messenger RNA, or mRNA.
This story was originally published on NBC News.