Editor’s note: The FDA and CDC have recommended a pause in the use of the COVID-19 vaccine from Johnson & Johnson (J&J). Nearly 7 million doses of the J&J vaccine have been administered, but the agencies are reviewing data involving six reported cases in the U.S. of a rare and severe type of blood clot called cerebral venous sinus thrombosis in combination with thrombocytopenia in people getting the J&J vaccination. All the cases were in women between 18 and 48, with symptoms developing six to 13 days after vaccination. ACIP will meet to further review these cases and assess their significance. 

These adverse events appear to be extremely rare, but COVID-19 vaccine safety is a top priority and health problems following vaccination are taken seriously. Those who develop a severe headache, abdominal pain, leg pain or shortness of breath within three weeks after J&J vaccination are being advised to contact their physician to assess them for the treatment required for this type of blood clot. (Updated April 13, 2021)

After receiving emergency use authorization from the Food and Drug Administration, Johnson & Johnson-owned Janssen Pharmaceuticals became the third company to make its coronavirus vaccine available in the country. The Johnson & Johnson (J&J) SARS-CoV-2 vaccine joins those made by Pfizer-BioNTech and Moderna to help prevent more severe COVID-19 outcomes, including hospitalizations and death.

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The J&J one-shot vaccine for adults is another major step toward vaccinating millions of people across the country. But the difference in efficacy rate compared with the vaccines produced by Moderna and Pfizer-BioNTech might raise questions for some Americans.

Two physician experts took time to share what patients should know about the J&J vaccine: AMA Chief Health and Science Officer Mira Irons, MD, and Sandra Fryhofer, MD, an Atlanta general internist who serves as the AMA’s liaison to the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices (ACIP). Dr. Fryhofer also is a member of ACIP’s COVID-19 Vaccine Work Group.


The J&J vaccine “is the first authorized vaccine to require one dose instead of two,” said Dr. Irons during an episode of the “AMA COVID-19 Update” about the new Janssen COVID-19 vaccine.

“The good thing about the Janssen vaccine is it's one dose and you're done,” echoed Dr. Fryhofer, a member of the AMA Board of Trustees. That means “you don't have to go back for a second dose. You don't have to make a second appointment. You can get fully vaccinated at one visit.

Sandra Fryhofer, MD
Sandra Fryhofer, MD

“But for our patients, that also means you’re only going to have one set of side effects,” she added.

“Don’t get caught up necessarily on the numbers game, because it’s a safe and effective vaccine and what we need is to have as many effective vaccines as possible,” said Dr. Irons. Rather than focusing on efficacy rates, “accept the fact that now you have three highly effective vaccines.”

“These vaccines have not been tested head to head, so it’s impossible to do a really accurate comparison,” she said. “What matters most is … they are all effective at preventing the most severe COVID outcomes, including hospitalization and death.”

Read about what to tell your patients when they ask which vaccine to get.

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While J&J’s vaccine has 66.3% effectiveness overall and 74.4% effectiveness in the United States, it has “100% efficacy against hospitalization and death from the virus,” said Dr. Irons. “That's really what we have to focus on.”

She noted that White House Chief Medical Adviser Anthony Fauci, MD, among other top experts are “saying is that it’s really important to focus on the severe end of the spectrum, preventing hospitalization and death.”

“No hospitalizations occurred in the vaccine group 28 days or more after vaccination as compared to 16 in the placebo group,” said Dr. Fryhofer. “There were also no COVID-associated deaths among those who were vaccinated. That’s pretty powerful.”

“When it came time for the Janssen vaccine trial, the background COVID incidence was higher,” said Dr. Fryhofer. “There were more variants circulating, including the variants of concern that can increase transmissibility and disease severity.”

“When the Janssen vaccine was tested, it was at the height of the pandemic,” she said. “The variants of concern were out there, so the test for the Janssen vaccine was harder—you can’t compare them.”

“If you look at the Janssen vaccine, the efficacy did vary across geographic regions,” said Dr. Fryhofer. “In the United States, it was 74.4% effective. In South Africa, it was only 52% effective and that’s where that variant B.1.351 was dominant.”

Discover what doctors wish patients knew about new coronavirus variants.

“Janssen’s viral vector platform is supported by an even larger body of evidence, including an Ebola vaccine that's already been tested in pregnant women and children and approved in Europe,” said Dr. Fryhofer. “More than 193,000 people—including patients of different ages and conditions—have been vaccinated with various investigational vaccines using this adenovirus platform.”

“The adenovirus vaccine uses a modified cold virus—an adenovirus called Ad26—as the viral vector and several genes have been removed from this virus,” she explained. “It’s replication deficient, so it cannot multiply in the body.”

This means that “it cannot give someone COVID-19,” said Dr. Fryhofer.  

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“The side effects are very similar to those for the mRNA vaccines, including injection-site pain, headache, fatigue and muscle aches,” said Dr. Fryhofer. “They didn't seem quite as severe as for the Moderna and Pfizer vaccines, but it is important to expect and be prepared for potential side effects.”

With most of the side effects occurring within one to two days following vaccination, Dr. Fryhofer recommends choosing a day or two when “you don’t have a lot of important stuff going on, because you might not feel well.”

Learn more from the AMA about what doctors wish patients knew about COVID-19 vaccination.

Since the J&J vaccine doesn’t require colder temperatures for storage as the Moderna and Pfizer vaccines do, “it’s more mobile, so it’s perfect for people who are homebound, that can’t—or won’t—go to a second appointment,” said Dr. Fryhofer. “It’s also good for people who move around a lot.”

“As I’ve talked to other physicians about this vaccine, one physician who provides health care for those in jails  and prisons said, ‘We have people constantly coming in and out of the system, it’s hard keeping track,’” she said. “So, this is one way we could give them this vaccine and feel good that they’re now fully protected.”

As with the Moderna and Pfizer COVID-19 vaccine trials, the J&J vaccine was tested with in large and diverse populations of patients. Nearly 44,000 people in South Africa, certain countries in South America, Mexico and the U.S. took part in the J&J testing.

“These vaccine manufacturers, when they’ve recruited participants, they’re thinking about diversity,” said Dr. Fryhofer. “They’re including people with different ethnicities and different geographies. They also include both older and younger people as well as those with underlying medical conditions.”

The AMA has developed frequently-asked-questions documents on COVID-19 vaccination covering safety, allocation and distribution, administration and more. There are two FAQs, one designed to answer patients’ questions, and another to address physicians’ COVID-19 vaccine questions.

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