The Food and Drug Administration (FDA) has issued an emergency use authorization (EUA) for a third vaccine COVID-19 in the United States, approving Janssen Biotech’s vaccine for administration to those 18 years and older.

“In making this determination, the FDA can assure the public and medical community that it has conducted a thorough evaluation of the available safety, effectiveness, and manufacturing quality information,” the agency announced on Feb. 27.1

As opposed to the two messenger-RNA vaccines already in use (Pfizer, Moderna), the new Janssen vaccine uses an attenuated adenovirus type 26 to target spike protein of SARS-CoV-2. A subsidiary of Johnson & Johnson, Janssen developed a vaccine that triggers antibody production after a single dose and can be stored in a refrigerator for approximately three months.

Clinical trials included 40,000 participants, with roughly equal numbers receiving either placebo or vaccine. Trial sites included South Africa, Mexico, and some countries in South America, meaning the vaccine was exposed to some of the circulating variants of the pandemic virus. This may explain its overall 66% efficacy in preventing moderate to severe/critical COVID-19 occurring at least 28 days after vaccination. That is lower than the mid-90s efficacy percentages found in the two preceding vaccines, but those clinical trials were conducted before the many virus mutations appeared. In addition, the vaccine prevented 85% of cases of severe infection.

“The most important goal for any of the vaccines that we are using is whether it prevents serious disease that requires hospitalization, perhaps intensive care admission, and death,” says William Schaffner, MD, nationally known vaccine advocate and a professor at Vanderbilt University. “We are less interested if it prevents [mild] disease that just keeps you at home.”

The most commonly reported side effects were pain at the injection site, headache, fatigue, muscle aches, and nausea. Most side effects were mild to moderate in severity and lasted one or two days.

“At this time, data are not available to determine how long the vaccine will provide protection, nor is there evidence that the vaccine prevents transmission of SARS-CoV-2 from person to person,” the FDA reported.


  1. Food and Drug Administration. FDA issues emergency use authorization for third COVID-19 vaccine. Feb. 27, 2021.