The J&J vaccine uses a different technology from the first two vaccines approved in the U.S.
Unlike the Pfizer and Moderna vaccines, which are mRNA vaccines, J&J’s is a viral vector vaccine. This means that the vaccine is delivered via an adenovirus, a type of virus that normally causes colds.
The adenovirus is engineered to include a snippet of SARS-CoV-2-DNA, which encodes the spike protein – the part of the coronavirus that latches onto cells. This snippet is then sent to your cells to produce mRNA, which tells your cells to make copies of the spike protein. Like the mRNA vaccines, this prompts an immune response.
“Your immune system recognizes the spike protein as abnormal and develops antibodies against it,” says Dr. Zucker. According to the CDC, people are considered fully vaccinated two weeks after getting the single-shot J&J vaccine.
U.S. studies found the J&J vaccine to be more than 70% effective against COVID-19.
Overall, the vaccine has a reported 66% efficacy rate in preventing moderate to severe disease from COVID-19, but in the U.S., the J&J vaccine had 72% efficacy. While this efficacy rate is lower than for the Moderna and Pfizer-BioNTech vaccines, which are around 95% effective, scientists believe this might be because the J&J vaccine was tested later than the Moderna and Pfizer vaccines. Therefore, there were more variant strains circulating when the J&J vaccine was tested than when the two other vaccines were tested, says Dr. Zucker.
The vaccine is still quite effective. “When the FDA first set out requirements for vaccination, 50% was determined to be acceptable. It certainly beats that. The bar has been raised by the mRNA vaccines,” he says. “At the same time, we’re not able to produce enough vaccine for everybody in the world, so there’s a benefit in having a vaccine that works well above the threshold we initially set and get more people vaccinated quicker.”
The J&J vaccine provides significant protection against severe illness and death.
In global trials, the J&J vaccine showed an 85% efficacy rate in preventing severe disease. Among the people who received the vaccine during the trials, after 28 days no one who contracted COVID-19 was hospitalized.
“The J&J vaccine offered complete protection against COVID-19-related hospitalization and death,” says Dr. Zucker. “Nobody in the vaccine trial group died. That is ultimately the outcome we care about the most.”