A U.S. Food and Drug Administration analysis of Johnson & Johnson's COVID-19 shot paves the way for it to become the third coronavirus vaccine authorized in the United States.
The data, released Wednesday, shows the single-dose vaccine is safe and effective.
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The Vaccines and Related Biological Products Advisory Committee — an independent panel of scientists — will meet Friday to issue recommendations on the vaccine. The FDA is expected to make a decision shortly afterward. The agency typically follows the advice of its experts, but is under no obligation.
If the vaccine receives an emergency use authorization, Johnson & Johnson will begin shipping doses immediately, company executive Dr. Richard Nettles told U.S. lawmakers Tuesday. The company expects to deliver 20 million doses by the end of March.
The FDA analysis included an international study involving 40,000 participants. That study found the vaccine to be 66% effective overall.
During the clinical trial, the vaccine was 85% effective at preventing hospitalizations and 100% effective at preventing death — findings that some experts say are the most important.
There have been some geographical differences in the vaccine's overall effectiveness. It was 72% effective in the U.S. and 66% effective in Latin America. But it was just 57% effective in South Africa, where a more contagious variant has become the dominant form of the coronavirus.
Clinical data suggests the variant, known as B.1.351, wasn't as vulnerable to the antibody response created by the vaccine.
The FDA found the vaccine to have a "favorable safety profile," meaning there were "no specific safety concerns" that would prevent it from receiving an emergency use authorization. The most common adverse reactions were injection site pain, headache, fatigue and muscle pain.
However, the agency noted there was some statistical uncertainty with some of the trial's data, including the finding that people over age 60 with medical conditions like heart disease and diabetes had a lower efficacy rating, of 42.3%.
Johnson & Johnson also estimated its vaccine is 74% effective against asymptomatic infections, though the FDA said there are some statistical uncertainties in regard to that estimate.
The ability to prevent asymptomatic infections is one of the biggest unknowns regarding COVID-19 vaccines. That capability would be a major advantage, given the role of asymptomatic infections in transmission.
Data has suggested the Pfizer and Moderna vaccines may be do so, but more research is needed.
Clinical investigators have said they are hopeful that the Johnson & Johnson vaccine is authorized as quickly as the Pfizer-BioNTech and Moderna vaccines were last year. A third vaccine — one that doesn't require two doses — would offer some much needed flexibility to vaccination efforts.
Johnson & Johnson is expected to deliver 100 million doses to the U.S. by June.
"With a J&J vaccine, we'll be able to accelerate the vaccine rollout for our country and for the world," Dan Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston, told The New York Times.
What are the differences in COVID-19 vaccines?
Is it better to receive one vaccine than the others? Scientists have stressed it is most important to have some protection against the coronavirus — and data shows all three offer that.
Here are some of the main differences between the three vaccines:
How they work: The Pfizer and Moderna vaccines use similar mRNA technology, relying on genetic code to trigger an immune response. The Johnson & Johnson vaccine uses a genetically-modified adenovirus that mimics the coronavirus's spike protein to produce an immune response. Non-modified adenoviruses cause the common cold.
Target populations: The Pfizer vaccine has been authorized for adults ages 18 and older. The Moderna vaccine has been authorized for people ages 16 and older. In clinical trials, the J&J vaccine was administered to people ages 18 and older.
Dosing: The Pfizer and Moderna vaccines require people receive two doses administered 21 and 28 days apart, respectively. Because Johnson & Johnson's vaccine only requires one shot, experts are hopeful that it can help expedite vaccination efforts and lessen the chance that more contagious variants become the dominant form of the virus.
Efficacy ratings: The Pfizer and Moderna vaccines each were about 95% effective during clinical trials. The J&J vaccine's efficacy is much lower, but it is still higher than the thresholds considered to be useful.
Side effects: The Pfizer and Moderna vaccines can cause pain, swelling and redness at the injection site, as well as chills, headaches and fatigue. In rare cases, severe anaphylactic reactions have occurred. The side effects tend to be more common following the second dose. The J&J vaccine may cause injection site pain, headache, fatigue and muscle pain.
Storage: The Pfizer vaccine must be stored in ultra-cold freezers for extended periods of time, but the FDA is now permitting it to be stored in standard freezers for two weeks. It can be kept in refrigerators for five days after thawing. The Moderna vaccine can be stored in standard freezers and remains stable for 30 days in refrigerators. The J&J vaccine can be stored for three months in regular refrigerators.