Johnson & Johnson’s COVID-19 Vaccine: Your Questions Answered

Here’s what to know about the single-shot vaccine and why a short pause had been recommended.

Johnson & Johnson COVID-19 vaccine

Photo by PHILL MAGAKOE/AFP via Getty Images

In February, the FDA granted emergency use authorization for a COVID-19 vaccine produced by Janssen Pharmaceuticals, part of the drug company Johnson & Johnson (J&J). The J&J vaccine, the third one authorized in the United States to help protect against COVID-19, is delivered in a single dose and can be stored at refrigerator temperatures for a long period.

However, in April, the CDC and FDA recommended a pause in the use of the J&J vaccine after they learned of six women who developed a rare and severe type of blood clot after receiving the shot. The pause lasted for 10 days as authorities reviewed data and evaluated recommendations.

Dr. Jason Zucker, an infectious disease specialist at NewYork-Presbyterian/Columbia University Irving Medical Center and instructor in medicine at Columbia University Vagelos College of Physicians and Surgeons, shares what you should know about the J&J vaccine, its safety, and what to watch for if you’ve already gotten the J&J shot.

The pause was a recommendation by the CDC and FDA “out of an abundance of caution.”

After initial reports that six women between the ages of 18 and 48 developed a rare blood clot within one to three weeks of vaccination, health authorities learned of nine additional cases in women and one in a man. Authorities reviewed the data and resumed the rollout of the J&J shot 10 days later, but with a warning added to its label about the risk for a rare blood-clotting disorder. “A review of all available data at this time shows that the J&J/Janssen COVID-19 Vaccine’s known and potential benefits outweigh its known and potential risks,” the CDC said in a statement.

“Pauses are common and allow health authorities to assess the situation and communicate with healthcare providers on recognizing symptoms and treating patients appropriately,” says Dr. Zucker. “A pause doesn’t mean that there isn’t an important role for this vaccine.”

If you’ve already gotten the J&J vaccine, don’t panic.

The overall risk of getting a blood clot appears to be about one case per million vaccinations (more than 8 million people having already received the J&J vaccine).

“The risk of these rare blood clots remains extremely low. The risk of getting COVID-19 in the United States is higher,” says Dr. Zucker.

The CDC recommends contacting your healthcare provider and seeking medical treatment if you develop any of the following symptoms:

  • severe headache
  • backache
  • new neurologic symptoms
  • severe abdominal pain
  • shortness of breath
  • leg swelling
  • tiny red spots on the skin (petechiae)
  • new or easy bruising
“The J&J vaccine offered complete protection against COVID-19-related hospitalization and death.”

— Dr. Jason Zucker

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.”